Traffic CrashInvestigations

A Training Guide forLaw Enforcement Officers

Wisconsin Department of JusticeLaw Enforcement Standards Board

December 2009

The Law Enforcement Standards Board approved this textbookon December 1st, 2009.

Training Academy effective date is May 1, 2010.

All law enforcement basic preparatory training courses that begin on or after May 1st, 2010, must incorporate this updated textbook and any related updates to the curriculum.

Courses beginning before that date may elect to use these updated materials.

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ACKNOWLEDGEMENTS

Many people have contributed to the writing of this manual. The Training and Standards Bureau, Wisconsin Department of Justice gratefully acknowledges the dedication of the Patrol Procedures Advisory Committee, which has worked long and hard to revise the content of earlier manuals and develop new content for the present guide. The current members of the Committee are:

Designated Representatives

Jeff Pettis, Sheriff’s RepresentativeTom Winscher, Chief’s RepresentativeClark Pagel, Wisconsin Technical College SystemPaul Matl, Wisconsin State PatrolCraig Henry and Chance Bamba, Milwaukee Police DepartmentDoug Funk, Milwaukee County Sheriff’s OfficeSherri Strand, Madison Police DepartmentStephanie Pederson, Training and Standards Bureau (Chair)

Practitioners

Monica Barman, Sun Prairie Police DepartmentBruce Buchholtz, Platteville Police DepartmentSteven D. Hausner, Burlington Police DepartmentKen Pileggi, Mukwonago Police DepartmentDeanna Reilly, Madison Police DepartmentTom Witczak, Fox Valley Technical CollegeHammond, Ken, Training and Standards Bureau

Emeritus (non-voting) Members

Colleen BelongeaTimothy HufschmidJay IdingBernie KocherDave MattheisenRobert MillerMike MurrayRichard Nichols

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TABLE OF CONTENTS

INTRODUCTION...............................................................................................................1TRAFFIC CRASH INVESTIGATION.................................................................1

Levels of Investigation..............................................................................................2At-Scene Investigation.............................................................................................2Advanced (Technical) Investigation.......................................................................2Collision Reconstruction..........................................................................................4Traffic Crash Investigation.......................................................................................4Investigator Qualities................................................................................................5

INVESTIGATING CRASHES..........................................................................................7REQUIREMENTS OF REPORTING CRASHES...............................................7

Wisconsin Statutes Regarding Accidents and Accident Reporting...................7RESPONDING TO CRASHES........................................................................10

Incident Response..................................................................................................10RESPONDING TO THE SCENE (Report).......................................................11

Arriving at the Scene..............................................................................................11EVALUATION OF THE SCENE (Evaluate).....................................................12SCENE STABILIZATION (Stabilize)................................................................12PRESERVE LIFE AND EVIDENCE AT THE SCENE (Preserve)....................14

Operator, Passenger, and Witness Interviews...................................................14Vehicle and Occupant Restraint System Inspection.........................................16

MECHANICS OF MEASURING AND DOCUMENTING CRASH SCENES.........19MEASURE AND DOCUMENT THE CRASH SCENE (Organize)....................19

Results at a Crash Scene......................................................................................20Vehicle Position.......................................................................................................20Debris areas.............................................................................................................20Road Marks..............................................................................................................23Meanings of Marks..................................................................................................30

LOCATING SPOTS FOR EACH RESULT.......................................................30MEASUREMENT SYSTEMS...........................................................................32

Coordinate System.................................................................................................32Triangulation System..............................................................................................34Combination of Systems........................................................................................36

MARKING SPOTS ON THE ROAD AND ROADSIDE.....................................37Marking Supplies.....................................................................................................37Marking Spots..........................................................................................................37

CRASH SCENE DIAGRAMS AND SKETCHES..............................................39Field Sketch.............................................................................................................39Labeling....................................................................................................................43

RECORDING BASIC MEASUREMENTS........................................................46Table of Measurements.........................................................................................46

MEASURING...................................................................................................47Measuring Devices.................................................................................................48Using Measuring Tapes.........................................................................................49

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Reading Tapes and Recording Measurements..................................................50Electronic Measuring Devices...............................................................................51

ADDITIONAL AND SUPPLEMENTAL MEASUREMENTS..............................52LABELING AND REVIEWING THE FIELD SKETCH......................................53AFTER-COLLISION SITUATION MAPS (SCALE DIAGRAM).........................53

Templates.................................................................................................................54Return the Scene to Normal (Normalize)............................................................55

SUMMARY......................................................................................................56WISCONSIN MOTOR VEHICLE ACCIDENT REPORT..........................................59

OVERVIEW OF WISCONSIN ACCIDENT REPORTS (Document and Debrief).........................................................................................................................59

Wisconsin Motor Vehicle Accident Report Form (MV4000).............................59Driver Report of Accident Form (MV4002)..........................................................67Badger TraCS and the MV4000...........................................................................69

DRIVER, VEHICLE, ROADWAY, AND ENVIRONMENTAL CONDITIONS AND FACTORS PRIOR TO THE COLLISION.........................................................71

Driver Condition.......................................................................................................71Roadway Conditions...............................................................................................71Environmental Conditions......................................................................................73

CONTRIBUTING CIRCUMSTANCES TO A CRASH......................................73Driver Factors..........................................................................................................74Vehicle Factors........................................................................................................74Highway....................................................................................................................74

SUMMARY......................................................................................................74PHOTOGRAPHING THE SCENE................................................................................77

CRASH SCENE PHOTOGRAPHY..................................................................77“AT SCENE” PHOTOS....................................................................................78

Basic “At-Scene” Photos........................................................................................78Photographing Vehicle Damage...........................................................................80Procedures for Photographing a Crash Scene..................................................81

OTHER CONDITIONS DEALING WITH PHOTOGRAPHY.............................82TIPS/Techniques.....................................................................................................82

SUMMARY......................................................................................................83APPROPRIATE ENFORCEMENT ACTIONS...........................................................85

PROCEDURES TO DETERMINE SPEED ESTIMATES.................................85ENFORCEMENT ACTIONS............................................................................85ENFORCEMENT DECISION...........................................................................86

OPTION #1: No Formal Enforcement Action....................................................86OPTION #2: Issue a Traffic Citation...................................................................86OPTION #3: Criminal Violations..........................................................................87Non-Contributing Violations...................................................................................87

HIT-AND-RUN INVESTIGATIONS..................................................................88SUMMARY.......................................................................................................................90APPENDIX A - GLOSSARY.........................................................................................91APPENDIX B - Wisconsin 2008 Traffic Crash Figures......................................103APPENDIX C – SLIDE-TO-STOP SPEED ESTIMATES.......................................105

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REFERENCES..............................................................................................................107

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INTRODUCTION

TRAFFIC CRASH INVESTIGATION

Our entire nation is a “nation on wheels.” Over 188 million motor vehicles and more than 170 million licensed drivers travel over two trillion miles a year on our streets and highways. 1 Hazardous materials are transported on these roads every day and thousands of people are killed in crashes on our streets and highways every year. Traffic jams and delays caused by traffic crashes during rush hour result in millions of dollars and hundreds of thousands of productive hours lost to the economy and unnecessary environmental pollution each year.

In 2008, 37,261 people were killed in the estimated 5,811,000 police reported motor vehicle traffic crashes, 1,630,000 people were injured, and 4,146,000 crashes involved property damage only.2 Since more people are killed and injured and more economic loss is suffered due to traffic crashes then all other types of crashes combined, the importance of traffic crash investigation cannot be overstated. The objective of this type of investigation ranges from providing the basic police functions, the protection of life and property, to restoring the flow of traffic.

A vehicle collision, regardless of driver intent, is referred to as a “crash” because the primary cause or causes typically result from specific driver actions. Traffic crashes are not accidents; they are avoidable events caused by a single variable or chain of variables.

There are three basic elements involved in any crash. The first is people. This includes, but is not limited to experience, impairment, and actions. The second is vehicles which includes, but is not limited to, size and equipment. The third and final element is the roadway. It also includes, but is not limited to weather (wet, dry, snow) and road conditions (road construction, debris). The investigating officer of the crash will have to locate and preserve any evidence from the collision found in or on the roadway.

Traffic crashes are extremely confusing events. How they occur, who or what caused them, and why they occurred are facts law enforcement must determine. Every officer must know the fundamentals of traffic crash investigation and know how to prepare traffic crash reports. Law enforcement officers spend a lot of time responding to, managing and investigating crash scenes. The Wisconsin MV4000 Report officially records events surrounding a crash. The accuracy and completeness of the report will depend on the quality of an officer’s investigation and his/her attention to detail. This area of instruction will introduce you to the

1 The Highway Safety Desk Book2 NHTSA Traffic Safety Facts (June 2009)

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necessity for accurate, impartial and professional traffic crash investigation and reporting.

Each subsequent level of investigation relies heavily on the quality of the initial investigation. The location of the crash, road conditions at the time of the crash, and other evidence at the scene cannot be replaced or recreated, unless documented by the officer during the at-scene investigation. The public, insurance adjusters, the Department of Motor Vehicles, and other involved personnel will see the results of the crash investigations. The quality of an officer’s work will reflect directly upon him/her as the investigator and on their agency.

Levels of Investigation3

The severity and circumstances of a collision will determine the proper level of investigation. In their order of complexity, the levels are usually called at-scene investigation, advanced (technical) investigation, and reconstruction. At-Scene Investigation

The first level of investigation is the at-scene investigation. When a basic crash occurs, the first responding officer will conduct this level of investigation and file a standard crash report. The at-scene investigator will collect evidence and document the scene.

The officer’s first task is to make the scene safe and prevent a second crash. Traffic must immediately be redirected. Next the officer must care for the injured and request additional resources if needed. Finally the officer will observe and record the facts pertaining to the collision. These include taking measurements, documenting other evidence at the scene, and completing a field sketch. The investigation may include taking photographs, checking all drivers for intoxication or other impairment, completing a Wisconsin Motor Vehicle Accident Report (MV4000) form, and other investigative reporting and documentation. The at-scene investigation is primarily concerned with data gathering and recording the scene.

Advanced (Technical) Investigation

At-scene investigations should be conducted for every collision. Advanced investigations are undertaken whenever the data obtained at the at-scene level is insufficient to complete the investigation. The purpose of the advanced investigation is to collect additional data for determining the charges to be brought against one or more of the individuals involved, for litigation reasons, or for laying the foundation for the next level of investigation – reconstruction.

3 International Association of Chiefs of Police. (September 2004) Highway Safety Desk Book: Traffic Collisions. p. 7-1 – 7-11.

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Unlike the at-scene investigation, which is initiated immediately or as soon as practicable after the collision, the advanced investigation may take place at a later time. Data from the at-scene investigation will be reviewed. Since much of the evidence at the scene may already have disappeared, the advanced investigation may depend heavily on the completeness and accuracy of the data recorded in the at-scene investigation.

During the advanced investigation the investigator is expected:

To determine the drag factor of the skid surface(s) and the minimum initial speed of each vehicle (unless already calculated in the at-scene investigation);

To determine time-distance relationships and solve momentum problems;

To match marks on the roadway with the parts on the vehicle causing damage, to determine the point of impact;

To determine what is impact damage to the vehicle and what is contact damage;

To match the damaged areas of the vehicles to determine the principal direction of force (PDOF);

To correlate injuries with the parts of the vehicle impacted by the occupants (occupant kinematics);

To determine if headlamps and other lamps were ON or OFF at impact;

To determine if any fire damage occurred before or after impact;

To determine if mechanical or electrical failure contributed to the crash (this may require the help of a specialist); and

To prepare a scale drawing of the scene from measurements and notes made at the scene.

Officers need to attend advanced training to learn the techniques used by the advanced investigator. A perquisite is usually the completion of a basic collision investigation course or several years of practical experience in at-scene investigation.

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Collision Reconstruction

Reconstruction is the highest of the three major levels of investigation and is usually undertaken only in support of litigation or research. Its main purpose is to determine how the collision occurred. It deals primarily with direct and immediate causes of the crash. These frequently entail behavioral errors on the part of the drivers.

Reconstruction expands on all the principles of at-scene and advanced investigation. It may involve experiments to ascertain performance and other capabilities of the vehicle, or to determine driver and pedestrian behavior. Reconstruction entails assembling all the technical data required to build a case for court.

Although a reconstructionist usually has greater depths of knowledge and broader experience than an investigator qualified only in at-scene or advanced investigations and can make more inferences from existing data, he/she is very dependent on the thoroughness and quality of the investigations conducted at the scene, and may have to work largely with the evidence that has been preserved and recorded earlier.

Traffic Crash Investigation

It is important to respond to crashes and to prevent further collisions. Your basic function as the responding officer is the protection of life and property. As the first responder, you have to protect your life as the top priority when responding to crashes. If you do not respond to the scene safely and protect yourself and the scene, you are of no value to anyone.

Often officers raise the objection that crash investigations merely do the job of the insurance companies. While it is certainly true that the insurance companies benefit from a good investigation, the fact that a traffic and/or criminal law may have been broken puts the responsibility directly in the lap of law enforcement to gather evidence for prosecution.

You have a responsibility to properly record all of the facts surrounding the crash. You may well be the only emotionally and financially detached person on the scene; therefore, your report of the event is logically the most accurate rendition of the event. All conclusions and any enforcement action you take must be based on the facts, evidence, and statements you personally gather or know to be true.

During the crash investigation, you have to determine the cause or causes of the collision. While the train of thought is that placing blame is not an objective of

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crash investigation, determining the cause or causes may in fact determine who bore the responsibility for the event.

Investigator Qualities

The qualities of a good crash investigator are those traits, both personal and professional, that the officer displays on each scene. You must be enthusiastic, sincere, responsible, and impartial when investigating a crash. You will find that traffic crash investigation, in real life, will sometimes be a fairly unpleasant task. Seldom will the people involved in the crash have anything to be happy about. However, the information in your reports may be useful in preventing future crashes through the application of education, engineering and enforcement. Some of the qualities you need to exhibit while investigating a crash will assist you in effectively completing the investigation while presenting a professional image of the law enforcement profession.

Many crashes occur in bad weather, resulting in you having to work while standing in the rain, bitter cold, or extreme heat. Through it all, you must not make a mistake or fail to carry out your assigned duties. The citizens you will be working with at the scene may be emotional, some may be rude, or they may be obnoxious. Because you are human, your initial response may be to lash out in anger, however, as a professional officer, you must try to rise above your frustration and anger and realize that this is an upsetting situation for the people involved in the crash.

You need to investigate all crashes thoroughly no matter how minor. It is easy for an officer to procrastinate and do the minimum acceptable on minor crashes. This is unacceptable to the people we serve. To the people involved, our customers, this is a very traumatic event. A motor vehicle is one of the single largest investments in many people’s lives and a major purchase to all. You need to show sincerity to the parties involved. For the people involved in a crash, this may be one of a very few contacts with law enforcement. You have it within your power to reap public support or lose it based on the level of professionalism you display.

Some important habits good investigators adopt include:

Be specific. Do not guess or estimate if measurements can be made. Evaluate what people say and distinguish fact from opinion. One hard

fact is worth a score of theories, conclusions, opinions, and inferences. Make personal observations and do not expect to learn all about the

collision from what people say. Write down information at the time and do not depend on memory. Write well enough so there will be no need for copying later. Take advantage of opportunities to get facts and avoid thinking, “I’ll get

that later,” because later is often too late.

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Prepare yourself for responding to traffic crashes before they happen. Some things you can do to prepare yourself include:

Know the territory. It is important to get to the scene of a collision quickly. Therefore keep maps, street guides or other directional aids handy. If you have firsthand knowledge of the roads in the area, that’s even better.

Learn what and where various organizations are who may have specific responsibilities with respect to collisions. Know the location of hospitals, towing services, and fire departments. A list of these, together with phone numbers and hours of the day in which their services are available is helpful and it is a good idea to become acquainted with some of the people in these organizations.

Acquaint yourself with other specialists who may be called to help investigate a crash scene (photographers, reconstructionists, etc.). Also, learn your department policy. If you are dispatched to investigate a collision, follow policies and rules dictated by your department.

Summary

This text will introduce you to the basic skills and steps to respond to a crash and begin the investigation at the scene. You will learn the procedure for measuring and documenting the scene at the first level of investigation; the at-scene investigation. You will not learn advanced techniques that traffic crash reconstructionists use, however, the information you learn to collect at the scene will directly affect any future investigation or reconstruction of the collision.

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Crashes, Not Accidents

Traffic crashes are not accidents, but are avoidable events caused by a single variable or chain of variables. Dedicated to reducing traffic injuries and fatalities by addressing the factors that cause them, the Bureau of Transportation Safety coordinates a statewide behavioral

highway safety program.

6

INVESTIGATING CRASHESREQUIREMENTS OF REPORTING CRASHES

There are two types of crashes: reportable crashes and non-reportable crashes.

According to Wis. Stat. 346.70(1) any crash must be reported to law enforcement when it results in:

Injury or death of a person. $1,000 or more total damage to property owned by any one person. Damages of $200.00 or more to government property (except motor

vehicles which must be $1,000 or more)

Note: If any party involved in a traffic crash dies within 30 days of the crash, the report will be a reportable crash.

If an officer cannot respond to the scene of a reportable crash (for example, during blizzard conditions when there are too many crashes for officers to respond to every scene), drivers should be instructed to file a Wisconsin Driver Report of Accident form (MV4002). This form will be covered in more detail later in the text. Only one report should be completed on the crash, however. If an officer completes the MV4000 Wisconsin Motor Vehicle Accident Report, drivers should not be instructed to complete the MV4002.

Wisconsin Statutes Regarding Accidents and Accident Reporting

The following are Wisconsin State Statutes relating to accident reporting and obligations of the operators involved in crashes.

346.66 Applicability of sections relating to accidents and accident reporting. In addition to being applicable upon highways, ss. 346.67 to 346.70 are applicable upon all premises held out to the public for use of their motor vehicles, all premises provided by employers to employees for the use of their motor vehicles and all premises provided to tenants of rental housing buildings of 4 or more units for the uses of their motor vehicles, whether such premises are publicly or privately owned and whether or not a fee is charged for the use thereof. These sections do not apply to private parking areas at farms or single-family residences or t accidents involving snowmobiles, all-terrain vehicles or vehicles propelled by human power or drawn by animals.

346.67 Duty upon striking person or attended or occupied vehicle. (1) The operator of any vehicle involved in an accident resulting in injury to or

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death of any person or in damage to a vehicle which is driven or attended by any person shall immediately stop such vehicle at the scene of the accident or as close thereto as possible but shall then forthwith return to and in every event shall remain at the scene of the accident until the operator has fulfilled the following requirements:

(a) The operator shall give his or her name, address and the registration number of the vehicle he or she is driving to the person struck or to the operator or occupant of or person attending any vehicle collided with; and(b) The operator shall, upon request and if available, exhibit his or her operator’s license to the person struck or to the operator or occupant of or person attending any vehicle collided with; and(c) The operator shall render to any person injured in such accident reasonable assistance, including the carrying, or the making of arrangements for the carrying, of such person to a physician, surgeon or hospital for medical or surgical treatment if it is apparent that such treatment is necessary or if such carrying is requested by the injured person.

346.69 Duty upon striking property on or adjacent to highway. The operator of any vehicle involved in an accident resulting only in damage to fixtures or other property legally upon or adjacent to a highway shall take reasonable steps to locate and notify the owner or person in charge of such property of such fact and of the operator’s name and address and of the registration number of the vehicle the operator is driving and shall upon request and if available exhibit his or her operator’s license and shall make report of such accident when and as required in s. 346.70.

346.70 Duty to report accident. (1) Immediate notice of Accident: The operator of a vehicle involved in an accident resulting in injury to or death of any person, any damage to state or other government – owned property, except a state or other government-owned vehicle, to an apparent extent of $200 or more or total damage to property owned by any one person or to a stat or other government-owned vehicle to an apparent extent of $1,000 or more shall immediately by the quickest means of communication give notice of such accident to the police department, the sheriff’s department or the traffic department of the county or municipality in which the accident occurred or to a state traffic patrol officer. In this subsection, “injury” means injury to a person of a physical nature resulting in death or the need of first aid or attention by a physician or surgeon, whether or not first aid or medical or surgical treatment was actually received; “total damage to property owned by one person” means the sum total cost of putting the property damaged in the condition it was before the accident, if repair thereof is practical, and if not practical, the sum total cost of replacing such property. For purposes of this subsection

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if any property which is damaged is held in a form of joint or multiple ownership, the property shall be considered to be owned by one person.

(2) Written report of accident. Unless a report is made under sub. (4) by a law enforcement agency, within 10 days after an accident of the type described in sub. (1), the operator of a vehicle involved in the accident shall forward a written report of the accident to the department. The department may accept or require a report of the accident to be filed by an occupant or the owner in lieu of a report from the operator. Every accident report required to be made in writing shall be made on the appropriate form approved by the department and shall contain all of the information required therein unless not available. The report shall include information sufficient to enable the department to determine whether the requirements for deposit of security under s. 344.14 are inapplicable by reason of the existence of insurance or other exceptions specified in ch. 344.

(3) Who to report when operator unable. Whenever the operator of a vehicle is physically incapable of giving the notice and making the report required by subs. (1) and (2), the owner of the vehicle involved in the accident shall give notice and make the report required by subs. (1) and (2). If the owner of the vehicle is physically or mentally incapable of giving the notice and making the report required by subs. (1) and (2), and if there was another occupant in the vehicle at the time of the accident capable of giving the notice and making the report, the occupant shall give the notice and make the report.

(4) Police and traffic agencies to report. (a) Every law enforcement agency investigating or receiving a report of a traffic accident as described in sub. (1) shall forward an original written report of the accident or a report of the accident in an automated format to the department within 10 days after the date of the accident.

346.73 Accident reports not to be used in trial. Notwithstanding s. 346.70(4)(f), accident reports required to be filed with or transmitted to the department or a county or municipal authority shall not be used as evidence in any judicial trial, civil or criminal, arising out of an accident, except that such reports may be used as evidence in any administrative proceeding conducted by the department. The department shall furnish upon demand of any person who has or claims to have made such a report, or upon demand of any court, a certificate showing that a specific accident report has or has not been made to the department solely to prove compliance or a failure to comply with the requirements that such a report be made to the department.

RESPONDING TO CRASHES

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When responding to reported crashes it is important that you remember the RESPOND acronym. The RESPOND model should be used as a guideline when responding to a crash scene. Trying to follow a fixed step-by-step procedure in responding to and investigating a collision can be as bad as having no plan at all. You must be flexible and respond to those things which need to be addressed first. You may also be able to accomplish a few steps listed below at the same time.

Incident Response

R Report Become aware Plan response Arrive/Assess Alarm/Inform

E Evaluate Look for dangers Determine backup needs Enter when appropriate/tactically sound

S Stabilize Subject(s) Scene

P Preserve Life - Conduct an initial medical assessment (as trained) - Treat to level of training - Continue to monitor the subject(s) Evidence

O Organize Coordinate additional responding units (if necessary) Communicate with dispatch and others Organize the collection of evidence (if appropriate)

N Normalize Provide long-term monitoring (as appropriate) Restore scene to normal Return radio communications to normal

D Document/Debrief Debrief self, other responding personnel, subject(s), other persons Document incident appropriately

RESPONDING TO THE SCENE (Report)

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When you become aware of a crash, plan your response to the scene. Obtain as much information as you can about the collision. Other information needed includes:

Location of the collision Time of occurrence What is involved Extent of injury and damage Obstruction of traffic Whether fire is involved Have ambulance, tow truck, fire equipment, and other investigators been

called? What assistance may be available

Based on this information, plan your route to the scene and consider possible things to be done upon arrival.

Employ safe driving techniques (drive with “due regard”) when responding and be aware that your attention may be diverted to thinking about what type of scene you will arrive at and what type of additional equipment you may need. You may narrow your peripheral vision, known as tunnel vision, which will prevent you from being fully aware of your surroundings. This may also occur to motorists as well as confusion and panic when they see and hear the emergency lights and siren. Not arriving on the scene due to becoming involved in a crash is of no value to anyone.

Have the emergency lights and siren activated when requesting the right of way from other motorists. Using the emergency lights and siren expresses your intentions to other motorists that the patrol vehicle is in an emergency mode. When responding, follow the shortest and quickest possible route to the scene.

Arriving at the Scene

When arriving at the scene select a safe location to park the patrol vehicle. You may need to use the patrol vehicle as a barrier to approaching motorists to protect the scene, victims and any evidence. The location of the patrol vehicle should be a safe distance from the vehicles involved and the emergency lighting should remain activated to warn approaching motorists of the hazard. At night you should park so the headlights illuminate the entire scene; however, you should not blind oncoming traffic with the patrol vehicle’s headlights at night.

EVALUATION OF THE SCENE (Evaluate)

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Upon arrival at the scene, watch for suspicious vehicles or subjects leaving the scene. The suspicious activity may be subjects who were involved in the crash who are fleeing the scene. They may be unlicensed drivers, have been involved in illegal activities, under the influence, etc. These vehicles may also lead to witnesses who otherwise would have been unknown.

As you look over the scene, begin to evaluate what challenges the scene presents. Look for dangers such as hazardous materials, vehicles on fire, downed power lines, etc. Also, try to determine how many injured people are on scene. Looking for these dangers and injuries will help you determine if you need to request any medical support, fire personnel, or other types of resources to respond to the scene.

Before you enter the scene, you need to evaluate if it is appropriate and safe for you to enter the scene. If there is a hazardous spill or downed power lines, the scene may not be safe for you or others to enter the scene, even if there are injured people. If you are hurt in the process of trying to reach the injured you will no longer be able to help them. Ensure you request any back-up or resources needed to make the scene safe, and wait for them to make the scene safe, before you enter the scene.

SCENE STABILIZATION (Stabilize)

As a first responding officer, you have to set priorities and make decisions at the scene. The officer in charge of the scene has to stabilize the scene as quickly as possible to prevent further injury to the people involved in the crash, officers or other motorists. The primary task you have on the scene is to check all subjects involved for injuries and provide first aid until more resources arrive on scene. Severely injured persons should not be moved, except to preserve their safety.

Traffic control is essential at a crash scene to prevent further crashes or injuries. Rerouting vehicles around the crash scene is the most common procedure used. Gathering crowds or unnecessary personnel should be cleared from the crash scene. You may have to request additional officers for crowd control or traffic direction/diversion at the scene. You may need to request that a utility company respond to the scene for downed power lines, gas line damage, and other utility related problems resulting from the crash. Additionally, requests may be made for tow trucks to remove non-drivable vehicles from the scene.

You may have to request additional equipment and/or officers due to the severity of the crash scene. The additional officer(s) may be used to close traffic ramps, intersections or entire roadways, assist in investigating the scene and other duties due to the crash size and severity of the crash. If the crash is severe, you may need to contact a crash reconstructionist or an investigator who is trained in more advanced traffic crash investigations than you are.

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Use flares and/or cones to assist in traffic control to maneuver traffic around or away from the crash site. (Figure 2-1) Use care when placing flares and do not place them near spilled flammable liquids. If the crash is around a blind curve or just over the top of a hill, put flares out before passing the view obstruction. You should also consider placing your vehicle or a second squad on the top of the hill or entrance into the curve with the emergency lighting on to alert motorists and give them time to slow down before approaching the crash site. This may be especially important if, for example, the crash site is immediately over the top of the hill in severe weather, such as an ice storm or snow storm. If motorists come to the top of the hill, see the crash site at the last minute, and slam on the brakes, they may hit ice or snow and lose control of their vehicle causing another crash.

Your responsibility is to stabilize and protect the scene; attempting to create the least amount of hazard to individuals at the scene as well as to oncoming traffic. Place warning devices far enough back from the scene to provide the oncoming motorists time to react properly.

• Angle cones/flares to channel traffic

• Angle squads if more than one (channels drivers and adds more light to scene)

• Alternate Cones and Flares if you have both

(Figure 2-1)

It is imperative that you and other responding officer(s) recognize the emotional and psychological effects that may be encountered by both the officer(s) and the subjects involved. The responding officer(s) must be aware of and prepared to act accordingly to prevent “becoming part of the problem”. Once at the scene, you and the other officer(s) must make rapid decisions as to vehicle placement with respect to protection of life and property and the accessibility of equipment.

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If the vehicles are in traffic and can be moved safely, the officer(s) should protect themselves and the motorists by moving them out of traffic on to the side of the roadway. This decision would be based on the nature of injuries and damage to the vehicles involved.

PRESERVE LIFE AND EVIDENCE AT THE SCENE (Preserve)

Once the scene is stabilized, your next step is to preserve life and evidence at the scene. This includes conducting interviews, inspecting vehicles and occupant restraint systems, and collecting and photographing other evidence at the scene.

Operator, Passenger, and Witness Interviews

Begin interviewing the operators, passengers, and witnesses to the crash. Prior to any of the parties involved in the crash leaving the scene via ambulance, attempt to obtain a statement as to what occurred. Due to the nature of some injuries, this may not be possible and the officer will have to interview the injured party or parties later.

Witnesses should be separated and interviewed separately. Do not allow witness to gather and exchange their stories about what occurred. Attempt to interview witnesses as soon as possible after the crash; they are under no legal obligation to remain at the scene of the crash. It is important that for each person interviewed you are tactful, patient, and employ good communication skills. Obtain identification from each person and record the information. Obtain statements from witnesses both verbally and then, if necessary, obtain a written statement from the witness. Have the witness sign their statement, as this is evidence obtained from the scene.

While interviewing, allow the person to tell his or her version of the events without interruption. Refrain from telling the person being interviewed “what happened.” Ask the person exactly where they were (their position), when the crash occurred. This may help to prove or disprove statements made later in the investigation. While interviewing subjects, pay attention to any signs or actions that suggest injury, illness, or any impairment.

When interviewing operators be aware of the person’s constitutional rights if the investigation leads into possible criminal wrongdoing. You may request that the operator(s) provide a signed written statement after the interview. This may assist you in future investigations.

When interviewing witnesses regarding the crash it is important to ask the witness questions regarding:

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Their positioning in relationship to the crash prior to the initial impact. If they observed the signal prior to the crash? Who had the red light? What did the vehicles do after the crash? Vehicle movement after the

crash. If they saw anyone flee the scene? If they saw who was operating which vehicle? The approximate speed of the vehicle or vehicles involved prior to the

crash. What was said by any of the operators immediately after the crash? If they observed any unusual actions by any of the vehicles prior to the

crash? If a pedestrian was involved, where was the pedestrian prior to the crash? What was the pedestrian doing? Were they running or walking?

These are some of the typical questions you may want to ask a witness regarding the crash. You may have more questions depending upon the type of crash involved.

When questioning the operator(s) some of the basic questions you should ask include:

Exactly where were you when you first saw the vehicle? (Point of awareness)

What were you doing at the moment you first saw the other vehicle? o Movement, speed, direction, speeding up or slowing down, turning,

backing, etc….o Attention – where were you looking? Talking? Other?

Where were you when you first realized you were in trouble? (Point of perception)

What were you doing at the moment you realized you were in trouble? (movement and attention)

Exactly what did you do, if anything, to avoid the crash? (possible evasive action)

Then what happened? Have the driver describe in his/her own words. Exactly where did the collision or first harmful event take place? (locate

unless known) Where did you stop after the collision (final position) What is the first thing you remember after the crash? (in his/her own

words)

If unconscious – What is the last thing you remember clearly before the crash?

o Verify story – do not press.o Establish trip plan as well as degree of shock/amnesia.o Note time period of unconsciousness.

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Who did you first see after the crash (clue to witnesses)o What did you say to him/her?

This list is not all inclusive, but it gives you a good starting point when asking operators about the incident. Depending on the circumstances you will have to ask more questions or may have to ask similar questions to those above, but not necessarily the exact questions above.

If the crash scene is serious in nature and additional officers are assisting with the investigation, the officer in charge of the scene should recheck the information that was obtained from the witnesses prior to the witnesses leaving the scene. Every officer has a different interviewing technique and he or she may not record all of the information that they have be informed of by the witness. This will reduce the follow-up calls that will slow the investigation.

Vehicle and Occupant Restraint System Inspection

There are several ways to identify a motor vehicle to distinguish it from all other vehicles. Identification is not the same as describing a vehicle as belonging to some class of vehicles.

A registration number is assigned by the state department of motor vehicles, displayed on the vehicle by registration plates and recorded on a registration certificate. Trucks carry additional registration numbers and trucks in interstate commerce are also registered by a federal agency and carry an ICC number in addition to a state number. All these can serve as additional items of identification but they rarely figure in traffic-collision investigations.

The Vehicle Identification Number (VIN) is the number assigned to the vehicle by the manufacturer primarly for registration and identification purposes. This number is sometimes called the “serial number” or “body number.” All vehicles, except for older vehicles, have the number embossed in part of the vehicle. It is readily visible to an observer standing outside of the vehicle without need of access to the vehicles interior.

In most cases, the VIN consists of not more than 17 characters stamped into a metal plate riveted to the deck of the instrument panel at the left side and visible through the windshield. Sometimes a vehicle is so badly damaged that the VIN in the usual place cannot be read. If it is important, look for the engine identification number (EIN) or transmission identification number (TIN). These may or may not be the same as the VIN.

A careful inspection of vehicle equipment and contents is necessary. Pay attention to any newly damaged parts of the vehicle and classify the type of

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damage. Be aware of old damage that was not caused during the current crash investigation. Items affecting vehicle control should be particularly checked, such as tires, brakes, lights, steering, signals and safety equipment. For example, it is important to know whether a tire blew out as a result of the crash or whether the tire blowout was a possible contributing factor of the crash.

Two types of damage that can occur on a vehicle:

Contact damage - damage caused by direct contact with some object that is not a part of the vehicle itself.

Induced damage - damage caused to vehicle parts that did not come in contact with the object struck, but resulted from the shock of the collision.

All damage observed should closely match objects that came in contact with that area of the vehicle. If you observe that the damage patterns do not match, investigate further.

Check for any signs of defective equipment that may have contributed to the crash. Some drivers may blame malfunctioning vehicle equipment for the crash, such as brake or tire failure. It is important that if the crash involves a fatality, the officers at the scene should not touch the brake pedal as they could destroy evidence from that vehicle without knowing it. That type of investigation should be left to the trained crash reconstruction officer. Make note of the reported mechanical defect and relay the information to the reconstructionist. Other mechanical defects may need to be inspected by a qualified mechanic. Less than one percent of all crashes are caused by mechanical failure yearly. Take detailed notes of mechanical failures and note them in your report.

Perform a detailed inspection of the vehicles involved in the crash. They should be performed to see if the vehicle needs to be removed from the scene by a tow truck. Inspect the vehicle for tire misalignment, bent suspension parts, fluid leakage, air bag deployment, broken windshield and other glass, missing headlights and taillights (if dark outside).

Inspect the interior of the vehicles involved in the crash. The inspection should include looking for view obstructions, dirty glass, open containers, improper mechanical devices (illegal steering wheels, pedals, etc.). Contents of the vehicle may also give important information concerning the identity, residence, occupation, destination and position of vehicle occupants.

The inspection should also include inspecting the radio. Was the radio volume turned up very high? If the battery on the vehicle was damaged you may not be able to check the radio volume. Where was the positioning of the headlight switch? Was it in the on position, off position or in the parking light mode? The operator may have been operating with their headlamps off in the evening hours.

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Do not turn the switch on or off as evidence in the crash may be destroyed. Note your initial observation when arriving on the scene.

You should also check for seat belt damage and usage. There may have been paramedics in the vehicle who removed the seat belts from the victims. Look at the webbing of the seat belt. Look for stains or markings that would not be on the seat belt if it were not in use.

Note the location of blood, fluids, dirt and glass. Look for fraying from the guide loop of the seat belt. The edges may show fraying from use. This may not be visible if you are looking at a new vehicle. Look to see if the belt buckle is accessible or is the belt tucked under the seat. Additional seat belt inspection should be performed by the crash reconstructionist if necessary due to serious injury or fatality.

Note the general condition of the interior of the vehicle. Were there items that interfered with the operator’s safe operation of the vehicle? Were there items on the dash that may have slid off the dash and interfered with the operator’s operation of the vehicle? Was there a lap top computer operating in the driver’s compartment? Was there any cell phone in operation and lying in the front seat area of the vehicle? These are all items that you should be looking for in the interior of the vehicle. With technological advances, people are operating vehicles unsafely while using electronic devices.

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MECHANICS OF MEASURING AND DOCUMENTING CRASH SCENES4

MEASURE AND DOCUMENT THE CRASH SCENE (Organize)

After stabilizing the scene, interviewing passengers, drivers, and witnesses, and checking the vehicles, you will investigate the scene in more detail and document your findings. This includes taking measurements, photographing the scene, and completing an Accident Report. The Wisconsin Motor Vehicle Accident Report Form (MV4000) will be the main form used to document the crash scene. While it is important to fill this form out completely, you should not use this form to drive your investigation on scene. Too many officers rely on this form to guide how they process the scene which may prevent them from doing a thorough investigation. This section will focus on evidence collection, measuring, drawing a field sketch, and photographing a crash scene. The Wisconsin Motor Vehicle Accident Report Form (MV4000) will be discussed a little later in the text.

The extent to which a collision can be reconstructed is dependent upon the evidence collected at the scene. Measurements taken at the scene are the foundation for speed estimates and other conclusions as to how the crash occurred. Your goal at the scene is to document the results of the collision so that a scale diagram can be drawn from your measurements and evidence collection. You should follow the steps listed below to process the scene first and fill out the MV4000 report towards the end of processing the scene.

There are eleven basic steps to follow when measuring and documenting the crash scene. These steps are:

1. Decide what results of the crash to locate at the scene.2. Decide what spots must be located for each of the results.3. Decide which system of measurement is best.4. Mark spots on the road and roadside.5. Start a field sketch.6. Prepare a table for recording basic measurements.7. Make measurements and enter them into the table.8. Decide what additional and supplementary measurements are needed.9. Make additional measurements.10.Review the field sketch and measurement records for clarity and

completeness.11.Complete the field sketch by identifying items in the sketch.

4 Baker, Kenneth, S. (2001) Traffic Collision Investigation. This entire section on measuring and documenting a crash scene is either directly from this source or adapted from Northwestern University Traffic Institute information.

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Results at a Crash Scene

Evidence obtained through interviews and vehicle inspections are only part of the information that needs to be collected at a crash scene. Investigators cannot rely on this information alone. Trauma, excited states of emotion, and shock can cause witnesses and victims to give inaccurate information. In fatal collisions, there may not be anyone left alive to explain what happened. Additionally, vehicle evidence may be confusing or hard to understand without looking at other results, such as damage to surrounding objects or roadway results. The word result refers to evidence such as debris, marks, damaged objects, vehicles, and other equipment, etc., at the scene.

You must first decide what results of the crash to locate at the scene. Carefully examine the scene noting the results of the crash, and any temporary conditions which may have contributed to the collision. Always be mindful that this may be the only opportunity to document this evidence. Once the scene is cleaned up the evidence may be gone forever. Results you should locate include:

The position of each vehicle and any bodies outside of the vehicle(s). Debris areas: significant vehicle parts and pedestrian possessions;

underbody dirt; liquid spatter, dribble, and puddles; and any other debris that came from a vehicle involved in the crash.

Scars (gouges and scratches) on the road, roadside, and on fixed objects.

Tire marks: skid marks, yaw marks, and collision scrubs. Parked vehicles which may have an obstructed view. Barricades and construction vehicles or materials.

Vehicle Position

Locate the final resting positions of all of the vehicles involved in the collision. Treat trailers as a separate vehicle regardless of whether or not it remains attached to the towing vehicle. For this purpose, motorcycles and bicycles are also classified as vehicles. Locate the positions of any pedestrians, motorcycle or bicycle riders, and ejected occupants whether deceased or injured.

Final positions of vehicles or bodies are classified as controlled or uncontrolled. Uncontrolled final positions are those reached by vehicles or bodies unintentionally after collisions. Controlled final positions are those to which vehicles or bodies are moved on purpose after a collision.

Debris areas

Locate debris at the crash scene. Various types of debris include dislodged vehicle parts and underbody dirt or snow. Liquid debris such as spatter, dribble, puddles, runoff, and soak-in may be present. Debris in pedestrian collisions may

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also include belongings such as hats, handbags or glasses, as well as blood or body tissue.

(Debris lying around the crash scenes)

Underbody Debris. Underbody debris in the form of mud, rust, paint, snow and sometimes gravel, sticks to the underside of fenders, engine body and other parts. In a collision this debris comes loose in two ways:

The metal to which it is stuck bends or crinkles and debris chips off. The shock of the collision loosens it.

After a collision, underbody debris may be heaped in a pile or it may be scattered thinly over a wide area. If the vehicle is moving when underbody debris is dislodged, the debris is also moving and does not drop straight down on the ground. It continues to move in the direction the vehicle was moving and at approximately the vehicle’s speed until it reaches the ground, unless it first strikes some part of the vehicle moving in another direction because of the collision. In these cases the debris is redirected. Because debris scatters so much it is usually a poor indicator of precisely where the collision took place.

Spatter (Vehicle Liquids). Spatter occurs when a vehicle container, such as a radiator, is collapsed by a collision with the result that liquid squirts out violently and splashes on the road and nearby vehicle parts. Such spatter areas are dark, wet spots, irregular in shape, and often composed of or surrounded by many small spots or “freckles.” Sometimes a lot of spatter makes an elongated “splash” pattern. Spatter reaches the road before the damaged vehicle moves very far and it is, therefore, a good indicator of where it was when the collision collapsed or broke open the liquid container.

Battery acid spatter. If the road is wet, battery acid spatter will not show. After it dries the spot where the acid struck the pavement may show quite plainly as a “bleached” area.

Dribble (Vehicle Liquids). Dribble is liquid draining – not squirting from a ruptured container on a wrecked vehicle. If the vehicle is moving, the dribble marks the path of the leaking part, usually from the point of maximum engagement to the final position. Rapid leakage and slow vehicle movement gives a conspicuous

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dribble path, sometimes continuous. Slow leakage and fast vehicle movement give an indistinct dribble path, often just a few scatter drops along the way.

Puddle (Vehicle Liquids). As soon as a vehicle that is dripping liquid stops moving, the dribble forms a puddle under the leaking part. This puddle shows where that part of the vehicle stopped. This is especially significant when the vehicle has been moved before the investigator arrives at the scene.

Run-Off (Vehicle Liquids). Run-off occurs when a puddle forms on sloping pavement. The liquid draining from the vehicle streams down hill.

Soak-In (Vehicle Liquids). Soak-in occurs where liquid is absorbed by soil or pavement cracks, either where run-off reaches the road shoulder or where the puddle forms off the pavement.

Tracking (Vehicle Liquids). Tracking of vehicle liquids results when tires roll through puddles, run-off, or spatter and, becoming wet, leave tire prints on the pavement as they roll on.

Liquid Cargo. Liquid cargo, usually from tank trucks, becomes debris when it is spilled on the road by collision. The position of the liquid cargo rarely makes any significant point in connection with the collision. If the spilled liquid is flammable, corrosive, or toxic, damage control may be the overriding consideration. Refer to the Emergency Response Guidebook when dealing with hazardous materials.

Spatter and dribble help locate collision positions. Dribble and puddles indicate where vehicles came to rest. Other kinds of liquid debris do not usually help much in determining how the crash happened.

Vehicle Parts. Compared to liquids which have come from vehicles, other vehicle parts are seldom significant as debris. Three important exceptions are:

Small parts found at the scene may help identify a vehicle that has left the crash scene. They may be useful therefore, in hit-and-run investigations.

Whole sections of the vehicle that have broken loose in collisions may be significant because of their final positions. This is the case when a vehicle breaks in two in a collision with a tree or when the engine is knocked out of a vehicle in a collision with a truck. The positions of these major parts are located by measurements in the same way that final positions of vehicles themselves are located.

Tempered glass from rear windows of vehicles may shatter into thousands of popcorn-sized pieces when the glass is broken in a collision. The glass forms a special pattern on the road, usually some distance from where underbody debris falls. When it breaks free, the glass continues to

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move and so the point at which it lands can be helpful in determining the direction of travel of the vehicle from which the glass came and sometimes the vehicle’s speed. Tempered glass debris areas are, therefore, quite worth noting and recording. Windshields, which are made of laminated glass, do not shatter and their after-collision positions usually mean little.

Solid Cargo. Solid cargo from trucks sometimes comes loose in a collision or before a collision. The point at which the cargo lands can be important in trying to find out the direction the truck was moving and something about its speed. Personal belongings and other cargo in the vehicle as debris rarely signify much about how the crash happened. They may help understand the nature of the trip and sometimes help in hit-and-run investigations. Granular cargo spilled as the result of a collision may be helpful in determining direction of travel and estimating speed. Roadside material scattered on the road after a collision will sometimes indicate where a vehicle came back on the road after running off, or how a collision on the shoulder took place.

Fixed Objects. Bent and broken guardrails, posts, trees, and other fixed objects can give some ideas of the speed of the vehicle striking them. Insignificant scrapes and scratches on roadside objects often reveal much about how a crash happened. Matched with damage or marks on vehicles, they fix the position of that vehicle at a specific point during the series of events that constitute the collision. They also help determine the vehicle’s path.

Road Marks

When operators react to an impending crash, their actions may cause tire marks on the road. Skid marks and scuffmarks have many characteristics in common. Both occur mainly when heat is produced by the tire rubbing on the road. When vehicles collide and skid across the road they can cause gouges and scrapes on the roadway itself. The following are examples of various types of results you may see at a crash scene:

Skid marks –A skid mark is made by a tire that is sliding without rotation on a road or other surface. Skid marks look different depending on the type of surface and its condition. Skid marks made on warm bituminous concrete may show up as heavy black smears that show some rib marks. The mark is largely composed of softened and smeared tar or asphalt. On cold, dry cement pavement, the mark may be a nearly invisible whitish track. Where the material does not soften with heat, the mark may be composed of rubber that is rubbed or ground off the tire, which, being tacky from heat, sticks to the road surface.

Normally in crash situations, the driver applies brakes very strongly and very quickly. This locks the wheels almost instantly and skid marks begin abruptly at very nearly the same time, with rear wheel marks beginning about the same

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place as the front wheel marks. If brakes are not fully applied quickly, each wheel may lock at a different time, so marks begin at quite different places. This is especially likely when the car has front wheel discs and rear wheel drum brakes.

Before the strong and definite mark appears, there may be an indefinite or questionable area which is sometimes called a “shadow” or “erasure.” In measuring the skid marks, the clear and distinct part is measured and recorded as observed. The faint and indistinct additional part, which may be imaginary, is measured and recorded separately. The distinct and shadow parts of the skid mark are combined when determining speed from skid marks.

Some examples of skid marks are:

(Braking skid marks)

Because of slower heating, due to a lighter load on them, rear tires may not begin to make skid marks as soon as the front ones. Rear tire marks usually do not begin a full wheelbase length beyond front ones. Rear tire marks sometimes begin further forward than front tire marks and in some instances may be mistaken for them. Sometimes rear-wheel skid marks are so exactly superimposed on front-wheel marks that you cannot determine whether the beginning of the mark was made by a front or rear wheel. When this occurs simply locate where the mark begins but do not describe it as either front or rear.

Skid marks do not last forever. Certain conditions can affect a skid mark, such as, the kind of mark, the weather, and the amount of traffic, road repairs or construction, and sometimes the special characteristics of the tire. Protect tire marks by keeping people away from them as best you can until you have studied them.

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Skip-Skids. Skip-skids in which the tire mark is repeatedly and usually regularly interrupted result from three conditions:

Bouncing semi trailers (most common) Road bumps Collisions (most significant)

A motor vehicle at point of collision will sometimes cause a shifting of weight from the front tires to the rear tires for a fraction of a second. When this occurs the rear wheels will leave a dark or darker mark for a short distance. The rear wheels may continue to bounce for some distance resulting in a skip-skid. Collision skip-skids are more likely to occur with small, light vehicles.

Gaps between the marks are usually only a foot or two long. The total length of the skip-skid should be measured and the measurement recorded. Be sure to describe the skid as a skip-skid. The length of each skid and gap should also be measured and recorded.

Gap Skids. In gap skids a set of skid marks ends, there is a gap, and another set aligned with the first begins. The gap is usually 10 feet or more in length. Gaps in skid marks are made by release of brake pedal pressure and its reapplication. Gap skids should be measured in the following manner. For each tire, measure and record the first skid mark, the length of the gap and then the length of the second skid mark, etc. This information should be recorded in sequence from where the gap skid starts and where it ends.

Collision Scrubs. Collision scrubs are not made by braking but by wheels momentarily kept from rotating by forces of a collision. They help indicate the point of impact. Collision scrubs are usually no more than 10 feet long and may present as a skid mark that changes direction abruptly. In same-direction collisions, they tend to be long and straight. In opposite-direction collisions they are likely to be short and curved. Sometimes, they are the only mark on the road that shows the collision point.

After-Collision Skid Marks. After-collision skid marks, made by tires or wheels which do not rotate for any reason, show the path of that tire precisely. The skid marks are usually curved after collision because the vehicle is rotating (spinning). The marks may vary in width from an inch to a foot, depending on how the tire is aligned in the slide. There may be gaps in after-collision skid marks as the wrecked vehicle rotates which puts more or less weight on the tire which created the gap.

Skid marks made by a locked wheel can be determined by looking at the striations. If the striations (scratches or rib marks) within the mark are parallel to the mark, the wheel is probably locked. Scuffmarks show the striations oblique (slanted) to the mark, because the wheel is rotating. The other way to determine

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whether the wheel was sliding or rotating is to examine the vehicle to find out whether the wheel was free to rotate, was locked tight, or could rotate with enough force to drag it on the road.

Yaw marks – A yaw mark is a scuffmark made on a surface by a rotating tire which is slipping more or less parallel to its axis. Sometimes yaw marks are called “critical speed” scuffs, or side slip marks. The difference between skid marks and yaw marks are that skid marks are made by braking, yaw marks are made by steering.

Yaw means that a vehicle is rotating about a vertical axis as it moves along a path. That means that the vehicle is not moving in the direction in which it is headed. In an ordinary turn, centrifugal force tending to keep the vehicle moving in a straight line is less than friction force between the tires and pavement. The rear wheels track inside the front tires. The vehicle follows the path in which it is steered.

In fast turns, centrifugal force becomes greater than the friction force between the tires and the road. Tires slip sidewise. The vehicle no longer follows the path in which it is steered. The rear wheels track outside of the front ones. The vehicle is no longer headed where it is going but heads more toward the inside of the curve. During a yaw, the vehicle may veer around enough to slide directly sidewise and then backwards.

Additional weight on the tires on the outside of the turn produces more friction heat and makes a stronger mark than the tires on the side of the vehicle toward the inside of the turn. The tire with the greater weight is not only overdeflected for that reason, but it is also side deflected to that most of the weight is concentrated on the outside edge of the tire.

The width of a yaw mark varies from one inch to as much as a foot. Striations in a yaw mark are not made by ribs in the tread. They are made either by gritty particles caught in the grooves or by tire sidewall ribs. Any striations that do appear are nearly crosswise of the mark at the beginning and they change to oblique (slanted) marks as the yaw progresses. If the mark goes far enough, striations become parallel to the mark. At this point the wheel momentarily stops rotating and the tire mark is a skid mark for a short distance.

Yaw marks are always curved because they result from steering. Ordinarily there are two marks from wheels on the outside of the curve, but on some material all wheels may show marks. If the yaw continues far enough, the path of the inside rear wheel crosses the path of the outside front wheel.

Simple measurements of the length of yaw marks are not of much use; measurements must be sufficient to plot the marks on a map. That means

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locating a point every 10 or 20 feet. When examining yaw marks, look for striations, and if they are visible, note their direction with respect to the mark.

(Yaw Mark)

Acceleration Scuffs – A scuffmark is made by a tire that is both rotating and slipping on a road or other surface. An acceleration scuffmark is made when sufficient power is supplied to the driving wheels to make at least one spin or slip on the road surface. One way to think about an acceleration scuff is to think about a race car or a vehicle in the movies that will peel out quickly from a stopped position. The vehicle may not move immediately because the tires are spinning with smoke coming out and then suddenly the vehicle shoots off quickly. This is an extreme example of how acceleration scuff marks are made, but it gives you a visual of how it happens.

(Creating Acceleration Scuff Marks)

Flat Tire Scuffs – A flat tire mark is a scuffmark made by an overdeflected tire, a tire which has too little air pressure in it for the load on it. The term overdeflected means a tire that is over-inflated or under-inflated. If a tire contains a quarter to three-quarters of its normal air pressure – it will be overdeflected and it will leave a mark, if any, that is heavy on the edges and light in the middle which looks much like a front wheel skid mark from a tire overdeflected by weight shift.

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Flat tire marks may extend for many miles along a road. You may not find exactly where a flat tire scuff really begins because the beginning is so faint. Completely flat tires have a somewhat different appearance. The tire bunches up and the sidewalls of the tire also touch the road. The mark made is scalloped and may show sidewall marks. When one of a pair of dual tires on one wheel goes quite flat, the other tire on that wheel may then be overloaded and overdeflected. Both tires can then make marks on the road.

Other tire marks. In loose material such as snow, sand, gravel, mud, or turf, both skidding and side slipping tires plow furrows. The material is shoved ahead or to the side, and the bottom is torn up and left rough and irregular. If the pavement has loose gravel or sand on it, this abrasive material may catch in the tire tread and leave scratches or grinding marks. This can happen when the road is wet, but the marks will not show until the road dries off.

Imprints – An imprint is a mark on a road or other surface made without sliding by a rolling tire. An imprint usually shows the pattern of the tire tread that made it. An imprint is sometimes called a print, impression, or deposit.

Road Scars – A road scar is any sign that the road, roadside, or a fixed object has been damaged or marred by a traffic collision. Road scars can be characterized as scratches and scrapes, towing scratches, gouges, chips, chops, grooves, grooves made by towing or scars on fixed objects.

Scratches and scrapes are light road scars made by metal and light pressure on the roadway. The vehicle or object making the scratch scrapes across the surface of the roadway and leaves a light mark on the road surface.

Gouges are pavement scars deep enough to be easily felt with the fingers. Types of gouges are chips, chops, or grooves.

Chips are short, deep gouges; a hole in the pavement made by a strong, sharp, pointed metal object under great pressure, usually without striations.

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Chops are broad, shallow gouges, even and regular on the deeper side and terminating in scratches and striations on the opposite, shallower side; a depression in the pavement made by strong, sharp metal edges moving sidewise under heavy pressure.

Grooves are long, narrow, pavement gouges; a channel in the pavement made by a small, strong, metal part being forced in some distance along the surface while under great pressure.

Falls. When a vehicle falls it is in the air for a short period of time. When a vehicle runs off a bridge or the top of a bank, it may travel through the air before it lands. In such a fall, there are no marks between where it left the surface and where it landed. This distance in the air is the best data for estimating speed when a car leaves the ground.

Careful observation of skid marks, tire prints or other signs of where the vehicle left the bank is important, but still more important is examination of the place where the vehicle first struck the ground again, especially if the vehicle continued beyond the spot. If necessary, measurements can be made of the slope at the take-off and the precise vertical and horizontal distances the vehicle moved through the air.

Flips. Flips occur when the moving vehicle hits something that stops the wheels suddenly. The vehicle then pivots upward and leaves the ground. Flipping means that the vehicle flips (rotates) over. The absence of any marks between take-off and landing is the important fact to establish. The signs of tire marks at the take-off point must be carefully located so must the signs of landing. Landing spots will be indicated by torn up turf or snow, crushed brushes, broken ice or damaged crops. The scar on the roadside where the vehicle landed is usually irregular and shallow.

Flips follow side slipping or yaw when the tire hits a curb or furrows. For speed estimation purposes, only the first of a series of flips is important. The take-off and landing points have to be identified and located as soon after the crash as possible because they may be obliterated in a short time.

Vaults. Vaults are endwise flips. They occur only when front wheels, sliding or rolling, are stopped by an obstacle, usually a curb, high enough and vertical so that the wheel does not roll over it. This means a height equal to three-quarters as high as the hub or more. Obtain measurements on exactly where the vehicle lifted off the ground and where it landed, whether it stopped there or not.

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Meanings of Marks

It is not important to determine exactly how all of the marks were made at the crash scene. If needed, the significance can be determined during a follow-up investigation or reconstruction. In order to determine the significance at a later date, it is important to locate the marks and describe them well enough so that such a determination may be made afterward by you or someone else.

Do not infer that because there are no marks left on the road there was no skidding or scuffing. Especially do not conclude that in the absence of such marks, there were no evasive tactics such as braking or steering. Vehicles with antiskid brakes, for instance, do not lock up the wheels and therefore do not skid.

Irregularities in either skid marks or yaw marks are important in determining how and where a collision occurred when a vehicle collides with another vehicle, a fixed object, or even a pedestrian or animal, its path is changed in some way, especially if it is skidding. If tire marks are being made at the time, the change in path usually shows in tire marks as a crook or a scrub of some kind.

In addition to the results of the collision, other evidence may be significant in a particular collision. This evidence is frequently temporary in nature, and should be located during the at-scene investigation. Parked or disabled vehicles may have contributed to a collision or presented a view obstruction. Positions where witnesses observed the collision should be located and temporary objects or conditions which may have contributed to the collision, such as ice patches, puddles, snow piles, barricades, and excavations should be located.

LOCATING SPOTS FOR EACH RESULT

After determining what evidence to locate, you must decide how many spots are required to position each object, or identify it accurately in your field sketch and through measurements. One spot may sufficiently locate small objects, however, larger objects such as vehicles or long tire marks cannot be adequately located with just one spot.

One spot will adequately locate relatively small objects such as:

A human body should be measured to the middle of the waist. Severed bodies will require one spot to locate each part.

Gouges less than three feet long or groups of gouges in an area less than three feet across can be located by the middle of the group, and supplement the measurements with photographs and a sketch detailing the gouges.

Grooves, collision scrubs and tire marks less than three feet in length could be measured to the middle of the mark.

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Contact damage or damage to fixed objects restricted to a small area less than three feet across can be located by one spot.

Spatter and puddles less than three feet across. Small debris areas less than three feet across. Vehicle parts such as wheels which have become dislodged.

Two spots are necessary to locate objects such as:

Vehicles. At least two spots are required to locate a vehicle. Undamaged corners along the same side of the vehicle are acceptable. Avoid using corners along the same end of the vehicle, as they are too close to accurately locate the vehicle. It is preferable to locate the wheels of the vehicle in lieu of the corners, particularly if the vehicle is stopped at the end of tire marks. This will also serve as the point establishing the end of the tire marks. Measure from the center of the wheel hub.

Straight tire marks. Locate each end of the tire mark. Curved tire marks greater than three, but less than eight feet in length.

Locate the ends. Straight grooves greater than three feet in length. Locate both ends. Contact damage or fixed objects extending over a great length. Dribble paths.

Three or more spots are required to adequately locate objects such as:

Curved tire marks greater than eight feet in length. Yaw marks (sideslip scuff marks) can reach great lengths with varying radii. Locate both ends and intermediate spots where the tire mark crosses a roadway edge, lane line or centerline. This may leave a long stretch without any spots. If this occurs, measure additional spots at ten foot intervals. If the mark is greater than thirty feet in length, ten to twenty foot intervals may suffice. Also, depending on the degree of the curve, you may need to mark spots at closer intervals to adequately depict the curve.

Straight marks with angles, such as crooks, gaps, or other irregularities. Locate both ends of each mark and any angle or irregularity.

Large debris areas. Measure three to six spots along the perimeter of the area. Include only the substantial deposits of debris.

A tire mark may change to a furrow upon leaving the pavement. Treat it as a single tire mark, locating both ends, the spot where it crosses the pavement edge, and any intermediate spots as necessary. Additional spots you should locate are where a tire mark, especially a curved tire mark, begins or crosses another tire mark, a roadway edge, a centerline or lane line, or a railroad track.

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MEASUREMENT SYSTEMS

After locating the results and spots, your next step is to decide what measurement system you will use measure the scene. The goal of measuring at the scene of collisions is to produce a scale after-collision situation map. Anyone should be able to take your measurements and draw a scale diagram without being familiar with the collision scene. If they are not able to do so, the measurements were not correctly taken. There are three methods you can use to measure the scene. The three methods are:

The coordinate system using a straight roadway edge as a reference line; The triangulation system which uses permanent landmarks as reference

points; or A combination method which uses a combination of the coordinate system

and triangulation system.

The coordinate system works best when you have a lot of straight line roads with gutters and curbs, such as on a city street, which you can use as reference lines and reference points. The triangulation method works better for scenes that are larger, are located at a curve in the road, or are in an area that does not include well developed roads. For example, you may use this method on a curvy, country road that has some permanent landmarks nearby, such as a farm house, water tower, or silo, etc. You can use these landmarks to triangulate the crash scene better than using the coordinate measuring system.

You may come across a scene where you must use a combination method; using the two separate systems to measure different parts of the scene. For example, you may have the main part of the crash scene located on a road that allows you to use the coordination method. However, you may have some sort of debris that flew quite a distance from the main crash site. You may find it easier to use the triangulation method to measure the debris that flew away from the main crash area. In this case, you use both systems to measure and document this crash scene.

Coordinate System

In Figure 3-1, there are three spots to be measured; you could use the two corners of the car if there is no damage on one side, or the preferred method, using the center of the wheel hubs, C1 and C2; and a body, B. Many officers will also measure the distance between the car and body. For example, it may be ten feet between the body and the end of the car. That locates neither the car, nor the body. Both can be anywhere on the map, as long as there is ten feet between them. However, if you describe point B as lying thirteen feet north of the south curb of Oak Street, and 46 feet east of the back of the sidewalk along the east side of Elm Street, there is only one spot where the body can be located.

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SIDEWALK

C

B

LAMP POST

OAK ST.

ELM ST.

N 13.0

E 46.0

RLRP

IMAGINARY EXTENSIONS

RL = S EDGE OAKRP @ E EDGE E SIDEWALK ELM

C1C2

FEET

0 10 20

Baker, K. S. (2001) Traffic Collision Investigation, p. 190

(Figure 3-1)

The coordinate method requires two measurements, or coordinates, to locate each spot. These measurements must be made from two permanent, easily identifiable landmarks. Anyone returning to the collision site should be able to reestablish these landmarks. You must select your landmarks before starting to measure.

In the coordinate method, one landmark is referred to as a reference line (RL), and the other as a reference point (RP). The reference point, sometimes called a zero point or starting point, establishes the origin (center) of your coordinates. The reference line is a line, either real or imaginary, which extends through or alongside the collision scene from which measurements can be made. The reference point must be a point on the reference line, or a point opposite a landmark near the reference line.

The reference line can either be a real or “natural” line such as the edge of the pavement. A natural reference line provides a visible, permanent line from which to measure. Such reference lines are easily described, and are seldom confused by others. However, the results of many collisions lie within an intersection where no natural reference line exists. In such instances, it may be possible to establish an imaginary reference line. The imaginary extensions of the roadway edges are most commonly used for this purpose.

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In addition to the two measurements required in the coordinate method, a direction of each measurement is needed. The directions, N, S, E, and W, are used for this purpose. Compass directions may be used; however, the more widely used method is to use nominal directions instead. The nominal direction is the general direction of the roadway. If you choose to use the “true” or compass direction, you should label your field sketch as such. You must record the direction of the spot to be located from the reference line to a point opposite the spot to be located.

When describing the reference lines, especially roadway edges, it should be clear which line was used. There may be several suitable reference lines along the edge of some roadways. A roadway bordered by a concrete curb and gutter with a painted edge line presents several options. If the curb is used as a reference line, the investigator should specify to which edge the measurements were taken. The vertical edge of the curb facing the roadway is referred to as the “face” of the curb. The edge of the curb which is adjacent to the roadside is called the “back” of the curb. Either edge is a suitable reference line for unmountable curbs; however it is usually easier to measure to the face of the curb. The back of the curb is the preferred reference line for roadways bordered by a mountable curb as the face is not readily discernable.

In the absence of a curb, the edge of the pavement is typically used as a reference line. Many investigators have used the painted edge line as a reference. These lines are typically four to six inches in width, and periodically repainted. The edge of the pavement provides a more precise and permanent reference from which to measure. When using these painted edge lines, measure to the middle of the width of the line. Irregular pavement edges require that the investigator use what seems to be an average or “best fit” as a reference line. Triangulation System

The triangulation method also requires that two measurements are made to each spot. When using triangulation, these measurements are from two reference points. A triangle is then formed by the spot to be measured and the two reference points. The measured spot is located at the intersection of the distances to each reference point. The distance between the reference points creates a triangle of which the lengths of all three sides are known.

Triangulation is useful in situations when it is not convenient to use the coordinate method. These situations include:

Roadway edges are indistinct or obscured, making them difficult to be used as a reference line.

Spots to be located are more than 30 feet off the roadway. The coordinate method requires that investigators sight a right angle between

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the spot to be measured and the reference line. It becomes difficult to accurately estimate the right angle when the distance from the reference line to the point is more than 30 feet.

Roadway edges are irregular or complicated, making them difficult to be used as a reference line.

Spots are located off the road where no natural reference line exists.

SIDEWALK

C

B

LAMP POST

OAK ST.

ELM ST.

C1C2

FEET

0 10 20

Baker, K. S. (2001) Traffic Collision Investigation, p. 199

HYDRANT

RP2

RP1

RP1 = HYDRANT S OF OAKRP2 = LAMP POST N OF OAK

28 FROM RP123 0 28 2

2

4 0

311

35 4

(Figure 3-2)

Locating spots by triangulation requires measuring the distance to a spot from two reference points, RP1 and RP2. To relate the reference points to the roadway, supplemental measurements are needed: The distance between the reference points, and the shortest distance from each reference point to the roadway edge. Reference points do not need to be on opposite sides of the roadway.

In figure 3-2, the reference points are described as RP1 = Hydrant S of Oak and RP2 = Lamp Post N of Oak; 282 from RP1. The distance to spot B is measured from both reference points. Spot B is 311 from RP1 and 354 from RP2. These distances form two sides of a triangle. The third side is formed by the distance between the reference points. It is 282 between RP1 and RP2. The location of spot B can be established by drawing a triangle with sides equal to the measured distances.

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The right angle (shortest) distance from each reference point to the pavement edges is needed to draw the reference point relative to the roadway. In figure 3-2, RP1 is 40 south of the south edge of Oak and RP2 is 230 north of the south edge of Oak. Measure these distances to the same edge of the roadway.

Triangulation is similar to the coordinate method in that it requires two measurements per spot. In fact, any method requires at least two measurements to locate a spot. Triangulation differs from the coordinate method in three ways:

No reference line is used. The two measurements are not necessarily at a right angle to each other. There is no need to specify the direction of each measurement.

Many of the same factors considered when using coordinate measuring techniques apply when selecting reference points for use in triangulation.

Safety. Select reference points which keep investigators out of traffic, and do not expose them to unnecessary hazards.

Proximity. Measurements are typically longer when using triangulation. If possible, select reference points which do not require measuring distances greater than the length of your tape. A 200 ft roll-up tape is particularly useful in triangulation.

Identification. Use easily identifiable and describable reference points. Anyone returning to the collision site should be able to reestablish your reference points.

Combination of Systems

The coordinate method is the preferred method of measuring at a crash scene. Triangulation provides a means of taking measurements when the coordinate method fails, or is not convenient. By no means are you restricted to using one method only at the scene of a collision. Circumstances may occur when both coordinates and triangulation are used at the scene of a collision. In these cases you may need to create a separate table for each set of measurements on your field sketch.

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MARKING SPOTS ON THE ROAD AND ROADSIDE

Marking Supplies

Sometimes you will need to mark roadway evidence, reference points, and other spots of interest. Spray paint is an effective way to mark spots on dry, hard surfaces such as the roadway. Bright orange works best for marking crash scenes. Crayons or chalk can be used to mark concrete or asphalt. Lumber crayons work well for this purpose. They are sold in various colors; however, yellow is the most common. Crayon marks are not as permanent as paint; however, they perform better on wet surfaces.

A small supply of nails will work well to mark spots along the roadside (in surfaces such as grass, dirt, etc.). To increase their visibility, tie a piece of flagging or attach an index card to the nail. Evidence cards are an effective means of marking the location of small evidence in photographs. Homemade cards or small orange cones used to mark athletic fields can also be used to identify evidence.

Marking Spots

After determining which measurements system you will use, mark spots on the road and roadside to help when taking measurements. Assign a letter to each item to be located. Try to use letters which are descriptive of the item they represent. For example, a truck may be labeled T, and a car in the same crash may be labeled C. The letter F may designate a Ford, and a C may designate a Chevrolet. Other letters that may be used to indicate other items include letters such as D for debris, G for gouge, or B for body. If there is no logical letter to represent an item, or it has already been used, any letter will suffice. However, avoid using vehicle or unit numbers that appear on the crash report.

Use numbers to denote multiple spots for the same object when more than one spot is necessary to locate an item. For example, the letter D may be used to identify a debris area, with points along the perimeter designated D1, D2, D3, etc. Long curved tire marks can also be labeled in this manner.

Figure 3-3 shows examples of how letters with numbers denote multiple spots for the same object.

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CC1

C2

S1

S2

S3

S4

S5

S6

10 FootIntervals

D1

D2 D3

(Figure 3-3)

You should mark the following spots:

Reference points when using coordinate measurements. Often your reference point is opposite a definable feature such as a utility pole or fire hydrant, at the imaginary extension of two roadway edges, or at the beginning of a curve.

Final rest position of bodies. Often pedestrians and ejected occupants are removed for medical treatment. Their final rest positions are crucial evidence in an investigation. Reestablish and mark their position(s).

The positions of two or more wheels of involved vehicles. Undamaged wheels are preferable. Ensure that if only two wheels are marked, they are from the same side of the vehicle. This will enable removal of the vehicles before measurements are completed. Other vehicles which should be marked are parked vehicles which are suspected of creating a view obstruction.

The ends of tire marks. The beginning of tire marks is not always easily seen. These marks may be more visible when viewed from different

December 200938

directions or angles. Marking the beginning of the tire mark will make it easier to measure.

The end of your tape. It may be necessary to measure a distance greater than the length of your tape. Mark the end of the tape, and move ahead. Write the distance to the point in crayon or paint.

Stations along the reference line. When measuring long curved tire marks, it is necessary to measure to points at 10 to 20 foot intervals along the reference line. Marking these intervals (stations) along the reference line makes taking these measurements easier and faster.

Significant evidence. The maze of tire marks, metal scars, and debris can be more easily deciphered if marked. Descriptions used on the field sketch can also be marked adjacent to the corresponding evidence. This will make measuring easier and quicker. Caution: Do not mark the scene if you are calling in a specialist or reconstructionist.

Circumstances will dictate whether marking the scene is necessary, and when it should take place. Whenever possible, try to take all the essential photographs before marking the scene. Photographs depict the condition of the scene following the crash. Additional photographs can be taken after marking the scene. The use of bright paint will increase the visibility of evidence in photographs. Marking the position of small evidence with evidence cards will also improve their visibility in photographs.

CRASH SCENE DIAGRAMS AND SKETCHES

Field Sketch

An at-scene investigation should include a field sketch. The field sketch provides a pictorial supplement to the at-scene measurements. It depicts the relative positions of the results of the crash and eliminates the need for lengthy descriptions.

The field sketch should include the results of the collision, roadway features, and significant objects which may have contributed to the collision. It is limited to factual data, and the investigator should not list opinions. Evidence such as collision scrubs, crooks, or metal scars should be clearly labeled. These may be indications of the point of impact. However, the point of impact is an opinion and should not be labeled on the field sketch.

The field sketch is a not-to-scale, free hand drawing. It is intended to supplement field measurements. Often the table of measurements can be included on the

December 200939

field sketch. Letters used to identify points in the table of measurements can be indicated on the field sketch next to the corresponding points.

The field sketch should be drawn while at the crash scene. It should fit on letter sized paper. Graph paper works well for this task. Do not crowd too much information on the sketch. Use additional paper if necessary, and consider placing the table of measurements on a separate sheet.

Roadway Skeleton

Begin the field sketch by placing a north arrow in an out-of-the-way corner of the field sketch. It is preferable to orient north toward the top of the sketch. However, since your paper is rectangular, there are instances when you may prefer to orient north toward the left or right edges. On roadways which do not run due north-south or east-west, the north arrow should indicate nominal north (the direction generally considered to be north).

Continue by drawing the roadway edges. This “skeleton” (Figure 3-4) will include only the pavement edges. Shoulders and returns (small radius curves which connect intersecting roadway edges) do not need to be drawn unless significant. Oblique roadway angles should be approximated, and large radius curves can be drawn straight. Show the alignment of the roadway edges as they are at the scene. Draw a dashed line through intersections to indicate aligned edges. Difference in roadway widths, and offset intersections should be depicted. Be sure to leave sufficient room to draw the results of the collision.

N

Baker, K. S. (2001) Traffic Collision Investigation, p. 218

(Figure 3-4)

December 200940

Identification

The field sketch should include the time, date, and location of the collision. The name of the person preparing the sketch, and persons assisting with measurements should also be included. If the measurements are not taken at the time of the collision, list the date and time the measurements were taken if done at a later time.

The location data should include the name of the street, road, or highway on which the crash occurred, the intersecting street, or distance from a definable intersection, and the city, or county and state in which the crash occurred. Many agencies assign a report, incident, or dispatch number to each collision or incident. This number should also be included on the diagram to further identify it. (Figure 3-5)

NC O L L E G E

N O RT H S T

B IRT

RIPO N , WIJ U N E 13, 2007. 3:45 PMS K E T C H B Y D . D O RNA S S IS T E D B Y D . K NA PP RE PO RT N O . 07-321

Baker, K. S. (2001) Traffic Collision Investigation, p. 218

(Figure 3-5)

Results of the Collision

After drawing a roadway skeleton, begin adding the results of the collision. Show final rest positions of the vehicles, pedestrians, and ejected occupants. Use a rectangle to indicate positions of vehicles. Specify the front of each vehicle with a triangle or an arrow. Draw diagonal lines from each corner of the rectangle to indicate an overturned vehicle. Stick figures are adequate to indicate positions of

December 200941

bodies. Show the approximate orientation of the body’s head and feet on the sketch.

Show tire marks on the field sketch. This should include not only pre-impact skid marks, but also post impact tire marks, yaw marks, and tire prints. Pay close attention to crossover points and try to approximate radii of curved tire marks. Indicate the approximate direction of striations in yaw marks and scuff marks by hash marks drawn across the tire mark. (Figure 3-6)

With Cross StriationsNo Cross Striations

Baker, K. S. (2001) Traffic Collision Investigation, p. 218

(Figure 3-6)

Add metal scars, debris, spatter, dribble, run-off and soak-in. Metal scars often appear in small clusters which may be difficult to fit on the field sketch. Consider creating a detailed sketch of this area with a separate table of measurements. Include the length, width, and depth of each scar in this table. A single point in the center of the cluster should be measured by coordinates or triangulation.

Include any fixed objects struck during the collision and indicate the area of contact to these objects on the field sketch. Show the location of any objects which may have contributed to the collision such as view obstructions. Their positions should be measured. In the case of parked vehicles, be sure to include the vehicle description on the field sketch. A Mazda Miata does not provide the same view obstruction as a Ford Excursion. Draw the position of any unusual circumstance such as construction zones (barricades, cones, etc.) and pavement irregularities (potholes, roadway debris, friction zones, etc.).

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Labeling

The features depicted on the field sketch must be labeled. Space constraints necessitate the use of abbreviations and alpha-numeric labels. More lengthy descriptions can be included on the table of measurements to prevent the field sketch from becoming too cluttered.

Choose logical letter descriptors for your field sketch. For example, the letter D may be used to label a debris field and G for a cluster of gouges. Use care not to duplicate any descriptors.

Begin labeling the roadway on which the crash occurred and any intersecting roadway(s) or drives. You may find it difficult to orient all text in one direction. It is okay to write some text vertically, but it is preferred to orient all text so it can be read from the bottom or right side of the paper. Avoid writing upside down or from the left side of the paper.

Label your reference line and reference point(s). Use the label “RL” for a reference line and “RP” for reference point(s) on the sketch. A complete description of each should appear either on the table of measurements or in a less cluttered area of the field sketch as shown below.

C T H C N

D ONO TPA S SRP

RL

MO

EN

LA

KE

RO

AD

1.5 M

ILE

S

T

T 1T 2

CC 1

C 2

A 1

A 2

B 1

Rhinelander, Wisconsin2:05 PM . N O V 25, 2007S K E T C H B Y M . D RA PK INRE PO RT N O . 501-059

Point N -S E -WT RU C K T 1 N 24.0 W9.7

T 2 N 20.0 W29.3C A R C 1 N 47.7 E 12.2

C 2 N 53.3 E 28.9F U RRO WS A 1 N 70.0 E 5.0

A 2 N 61.2 E 15.0B 1 N 56.3 E 10.5

RL = E E D G E C T H CRP = O P D O NO T PA S S S IG N

Baker, K. S. (2001) Traffic Collision Investigation, p. 220

(Figure 3-7)

Label the rest position of each vehicle. A letter descriptor is adequate for the field sketch and a more complete description can be included in the table of

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measurements. Indicate the points on the vehicle to which measurements were made. Use a numeric suffix to identify individual points. For example, in the sketch above, T1 indicates the left front wheel of the truck and T2 indicates the left rear wheel.

Give each tire mark a separate letter descriptor. Use numeric suffixes to identify multiple points on the same tire mark. A more complete description of each tire mark should be included in the table of measurements. Label multiple points around the perimeter of large debris fields. Small debris areas may require only one point. Clusters of metal scars require a single point to be labeled. However, long scratches or grooves may have to be labeled in the same manner as a tire mark. Consider labeling multiple points around the perimeter of large scrapes when necessary.

Roadway dimensions such as road and lane widths can be labeled on the field sketch. Offsets at intersections and curve radii can also be dimensioned on the field sketch. Use care though and do not clutter the field sketch. If necessary, include these dimensions on a separate field sketch depicting only the roadway features. The field sketch may also include the type of pavement (asphalt, concrete, etc.) and surface condition (wet, dry, etc.).

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ROAD FEATURES SIGNIFICANT ROADSIDE OBJECTS

ROAD USERS SIGNS OF CRASH ON ROAD

TRAFFIC CONTROL DEVICES ADDITIONAL USEFUL SYMBOLS

ROADWAY EDGEWITHOUT CURB

CURB

SHOULDER EDGE

SINGLE GUARD RAIL

DOUBLE GURAD RAIL

MASONRY SEPARATOR,BRIDGERAIL, PIER

CORRUGATED RUMBLE MEDIAN

RAILROAD TRACKS

PROPERTY LINE

UNMARKED CENTER

MANHOLE, INLET, DRAIN

X X X X X FENCE

STEEP BANK (PointsDownhill)

DITCH

STREAM, POND, LAKE

UTILITY POLE

TREE,UNOBSTRUCTED VIEW

SHRUBBERY, TREE(OBSTRUCED VIEW)

LAMP POST, HYDRANT

CROPS(OBSTRUCTED VIEW

BUILDINGS

.

.

v v v v v v v vv v v v v v v

v v v vv v v

PERSON UPAND DOWN

CYCLE UP ANDDOWN

VEHICLE UPRIGHTAND OVERTURNED

TRUCK

BUS

TRACTOR AND SEMITRAILER

PARKED VEHICLE

SKIDMARK

YAWMARK

OTHER TIRE MARKS

TIRE SCRUB

FURROS

SPATTER & DRIBBLE

PUDDLE & RUNOFF

OTHER DEBRIS

GOUGES

SCRATCHES, SCRAPES

BROKEN LANE LINE

BARRIER LINE

LANE REFLECTORS

TRAFFIC SIGN

FLASHING SIGNAL

TRAFFIC SIGNAL

RED

NORTH ARROW

SCALE

GRADE (FT/FT)+ IS UPHILL

SIGHT LINE

CAMERA POSITION

FEET0 10 20

-0.02

. . . . . . . . .

. . . ... ........ . . ... .......

STOP50

MPH

Baker, K.S. (2001) Traffic Collision Investigation, p. 245

(Figure 3-8 Recommended symbols for use on field sketches.)

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RECORDING BASIC MEASUREMENTS

Table of Measurements

You will need to record numerous measurements at the crash scene. To avoid cluttering the field sketch, create a table of measurements. This table can appear on the field sketch or you can place it on a separate sheet to supplement the field sketch. The table organizes the information and helps ensure that no measurements are omitted.

First, decide if the table of measurements will fit on the field sketch. If there is any doubt, place it on a separate sheet of paper. When using a separate sheet, repeat the reference point(s) and reference line descriptions and crash identification information on the table.

Next determine whether coordinate measurements or triangulation will be used to measure the scene. In some cases more than one method will be used. It may be necessary to use two reference lines or use both coordinate measurements and triangulation. A separate table of measurements is needed for each set of measurements.

The table should be divided into columns. Label the first column “Spot” or “Spot Description.” It should include the corresponding alpha-numeric descriptor used on the field sketch. This column may be used to provide additional spot descriptions such as skid marks, debris, gouges, etc. The second and third columns are used for measurements.

For coordinate measurements, the second column will be used to record north and south measurements and the third column will be for east and west measurements. Label each column as “N-S” and “E-W” respectively. Remember to use nominal directions as previously described. For triangulation, the second column will be used to record the distance to reference point 1 (labeled RP1) and the third column will be used to record the distance to reference point 2 (labeled RP2). (Figure 3-9)

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PO IN T N -S E -WF O RD F 1

F 2D O D G E D 1

D 2S K ID MA RK S A 1

A 2A 3

RL = E E D G E WE L S H IRERP@N E D G E S PRU C E H IL L D R

PO IN T RP1 RP2S A T U RN S 1

S 2PO N T IA C P1

P2S K ID MA RK S A 1

A 2G O U G E G

RP1 = U T IL IT Y PO L E 5406RP2 = H Y D RA N T S E C O RN E R

Baker, K. S. (2001) Traffic Collision Investigation, p. 221

Coordinate Method Table Triangulation Method Table

(Figure 3-9)

The field sketch should include only factual data. It is a record of your observations while at the scene. No opinion or conclusions should be depicted. Things that should not be listed on a field sketch include:

The point of impact (or POI) is an opinion, not an observation and should not be listed on the field sketch.

The paths traveled by the vehicles before and after the collision should not be depicted on the field sketch. These paths are also an opinion and not an observed fact. Tire marks should be listed, but do not list the direction of travel on the sketch.

There are data recorders (handheld instruments) that record data at a crash site and can then be downloaded into a computer. Computer software then uses this data to create a drawing after the survey. However, this does not eliminate the need for a field sketch. Complete a field sketch to aid the instrument operator in assigning description codes to various features.

MEASURING

The basic equipment needed for scene measurements is minimal. To help prepare the field sketch you need a clipboard, paper, and a writing instrument. Grid paper will make it easier to draw a field sketch and maintain proper alignment of features depicted. The grid will also help create the table of measurements. The writing utensil should be a good mechanical pencil (have

December 200947

extra lead available). You will also find the need to erase items from your notes. A good plastic eraser works better than the traditional red rubber eraser. The inability to erase and poor performance in wet and cold conditions make ink pens impractical.

A micro-cassette recorder is an invaluable piece of equipment. Observations can be easily and rapidly recorded at the scene of the collision and transcribed later. The recorder performs well in the rain and snow, but may not work well in extreme cold. However, using a recorder to take measurements should not be done except by experienced investigators. It is better to write down the measurements while still at the scene of the collision. If you record these measurements verbally versus writing them down, you run the risk of omitting needed measurements. A micro-cassette recorder is also useful for recording witness and driver interviews, but be sure you follow the proper procedures for taping these interviews according to your department policy.

Measuring Devices

A variety of measuring devices are available. The bare minimum should include a 100 foot roll-up tape and a 25 foot tape measure. Fiberglass roll-up tapes are usually available in 100 foot and 200 foot lengths. A 100 foot tape is usually sufficient. The roll-up tape works well with both the coordinate and triangulation measurement methods. When using the coordinate method, string the tape along the reference line with the zero-end at your reference point. If the surface is flat, and it is not too windy, a pin, a nail, or weight can be used to hold it in place. Distances along the reference line can easily be read from the tape. The tape can also be used as the reference line when extending roadway edges or measuring along curves.

When using the triangulation method, the distance from each reference point to the point to be measured frequently exceeds 25 or 50 feet. Try to select reference points within 100 feet of the points to be measured. If this is unavoidable, use a 200 foot roll-up tape if you have one on hand.

A spring loaded pocket tape measure is useful for measuring short distances. They are available in lengths from 3 to 30 feet. The longer the tape the more useful it will be, however. Tape measures are most useful when using the coordinate method of measuring. To ensure that a right angle measurement from the point to be measured to the reference line is obtained, the distance should be kept less than 30 feet. Tape measures are also invaluable for documenting vehicle dimensions and damage measurements.

Measuring wheels are ideal for long measurements over clean, smooth surfaces. Measurements can be made by one person and more quickly than with tape. However, these wheels follow the terrain which makes them useless for measuring over uneven surfaces such as ditches. Measuring wheels do not

December 200948

work well on snow or ice either because they depend on friction to turn the wheel. As a whole, they are not as accurate as tape and they should be considered as a supplemental piece of equipment and should not be used in lieu of a measuring tape. Using Measuring Tapes

Short distances are easily measured with the tape measure. Under most conditions, it can be operated by one person with one hand. The end of the tape measure can be hooked on edges or butted up against a vertical surface. It is well suited for measuring:

Vehicle dimensions. The length, width, wheelbase, track width, and overhangs are typically less than the length of the tape measure. The preferred units for vehicle dimensions are in inches.

Height and sizes of signs. Height of curbs, roadway drop-offs or lips, and depth of potholes. Width of sidewalks, or other improvements. Lengths and widths of metal scars. Distance of points to the reference line in the coordinate method.

For distances over ten feet, it becomes difficult for one person to use the tape measure. Have an assistant help you take measurements. Anyone capable of holding the end of the tape can help, but if you can find someone with experience the process will not require you to give much guidance.

If both investigators are experienced, either can record the measurements. It is usually quicker if the investigator recording the measurements holds the zero-end of the tape. This frees him/her to write down the distance while the assistant handles rolling up or retracting the tape and moving to the next point. It is imperative that the measurement is recorded accurately. The investigator recording the measurement should repeat the distance to the assistant for verification.

Roll-up tapes are used for longer distances. When using the coordinate method, extend the roll-up tape along the reference line. If possible, use a chaining pin, nail, or weight to secure the zero-end of the tape at the reference point. The tape should be sufficiently secure to permit the tape to be pulled taut during measurements. An assistant may be required to facilitate this. The roll-up tape works well measuring distances along the reference line to the reference point.

If your reference line is the extension of a roadway edge, the roll-up tape can be used to provide a line to which to measure. Line up the tape with the roadway edge and extend it into the intersection. When possible, extend the tape to meet the aligned edge on the opposite side of the intersection. This will eliminate any errors in sighting the roadway extensions.

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When measuring a curved roadway with a large radius as a reference line, a roll-up tape can provide a straight line to which to measure. It is not possible to measure along a curve with a tape. Instead, extend the tape across the curve. The zero-end of the tape should be at the reference point.

Triangulation usually involves distances over 25 feet to one or both reference points. For this reason, the roll-up tape is better suited for this method. It is usually quicker to measure to all points from one reference point, then switch to a second. Care must be taken to measure the identical point from each reference point, ensuring that no measurements are omitted.

Distances should be measured horizontally, or level. Small roadway grades do not introduce large errors in short distances. However, when measuring over uneven surfaces such as ditches, the tape must be pulled taut and kept level. Measure to the center of poles, fence posts, trees, fire hydrants, and circular or rectangular objects on or adjacent to the roadway such as manholes, and inlets. This is the conventional practice, and well be assumed by others unless otherwise specified.

When locating final rest positions for vehicles, measure to the center of the wheels or corner (acceptable but indicate this clearly). Measurements to undamaged areas are preferred, but nothing prevents you from measuring to all four wheels or corners. Measure directly to the outboard edge of the tire directly below the axle or to the corners. It is often easier to measure the final rest position after the vehicle has been removed. Ensure that its location is properly marked and that your marks will not be obliterated during the vehicle’s removal. It is common to measure to the center of tire marks. If for any reason this practice is not followed, be sure to indicate on the field sketch the exact point to which the measurement was made.

Reading Tapes and Recording Measurements

Measuring devices using imperial units are graduated in feet and tenths, or feet and inches (twelfths). Both units may be printed on one tape. Feet and tenths are used by engineers and surveyors and are the preferred units for measuring at crash scenes. Inches are the preferred units for vehicle dimensions and damage measurements. Check your tapes to determine which units are on them. If your tape(s) contain both, decide which units you will use and ensure that anyone assisting you is aware of this.

When using units of feet and tenths, simply record the distance with a decimal point between. For example, the distance of 2 feet and 7 tenths should be written as 2.7. For distances less than 1 foot, it is common practice to write a zero before the decimal point. For example, the distance of 6 tenths would be

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written 0.6. The zero before the decimal point reduces the possibility of confusing this distance with six feet.

The method of writing feet and inches varies from one discipline to the next. A usual way to indicate feet and inches is to use the prime (‘) for feet and the double prime (“) for inches. However, the prime symbol can be confused with the number 1. For this reason, this method is not used in crash investigations. If inches must be used, indicate that by superscripting and underlining the inches. For example, six feet, 5 inches would be written, 65. When recording distances less than one inch, include a zero before the distance as in 08 to eliminate confusion. Some tape measures are graduated in inches only. Follow the same convention of including a zero before the distance. For example, the distance 78 inches would be written 078.

Accuracy (how close a measurement is to the actual distance) is important in crash investigations. Measurements should be made to the nearest tenth of a foot. To indicate that a distance was measured to the nearest tenth, record the first digit to the left of the decimal point, even if it is a zero. The distance 5 feet should be recorded as 5.0.

Errors in accuracy usually result from carelessness. Common errors in measuring are:

Reading numbers upside-down, for example mistaking a 9 for a 6. Misreading the foot mark, such as reading 15.6 as 14.6 or 16.6. Confusing the location of zero on your tape. (Not all tapes are imprinted

with a zero at the free end.) Losing count of the number of complete tape lengths measured. Forgetting to reset the counter on a measuring wheel. Attempting to remember distances rather than recording them

immediately. Adding separate distances mentally rather than recording each

measurement separately and adding them later.

Electronic Measuring Devices

An electronic distance meter (EDM) uses light to measure the distance between the instrument and the point to be measured. This requires a line of sight between the instrument and the point. The light beam, or signal, is reflected back to the instrument. This can be accomplished by two methods.

The first type of instrument uses a reflective target. The target is sighted by a telescope mounted to the EDM. This type of instrument is extremely accurate and the range varies by instrument, but 1000 feet per prism is typical. The more likely method uses reflectivity of an object to return the signal to the instrument. Laser speed measuring devices used in traffic enforcement are also capable of

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measuring distances. This works well when shooting distances to vertical surfaces, but becomes difficult to measure to points lying on a horizontal plane. A vertical target held over the point will make measuring these points easier.

Electronic distance meters are most useful when using triangulation. The instrument is held over the point to be measured and the distance to each reference point measured. Coordinate measurements can be performed, however, with more difficulty. Before you use either of these methods, you must attend additional training to learn how to operate and properly take measurements with the equipment.

ADDITIONAL AND SUPPLEMENTAL MEASUREMENTS

Review your field sketch and table of measurements. Ensure all of the basic measurements are complete. In some cases you may need to take additional measurements to identify evidence not covered in the basic measurements. You may also want to include a detailed sketch of evidence, such as metal scars on the road, which should include supplemental measurements. These supplemental measurements include length, width, and depth of the scars. Create the detailed sketch on a separate sheet of paper than the field sketch.

IN C H E S

L W D

1 G RO O VE 6 ½ 1/ 162 S C RA T C H 11 ½ 03 S C RA T C H 15 ¼ 04 S C RA PE 5 1 05 G RO O VE 7 ¾ ¼6 S C RA T C H 4 1/ 8 07 C H O P 10 1-1/ 2 1/ 8

12

3

45

6

7

Baker, K. S. (2001) Traffic Collision Investigation, p. 219

(Figure 3-9 Detailed sketch with supplemental measurements)

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LABELING AND REVIEWING THE FIELD SKETCH

The features depicted on the field sketch must be labeled. Only printed text should be used (no cursive). Lettering templates and lettering guides are available but hand lettering is acceptable. The text should be oriented so that it can be read from the bottom of the page. There may be instances where it is more convenient to orient text so that it can be read from the right edge of the paper, however.

As stated earlier, identifications should include the name of the roadway on which the crash occurred, the intersecting street or distance from a definable intersection, the city (or county) and state where the collision occurred, and the time and date of the collision. Additionally, the name of the investigator preparing the sketch should be listed along with the report or reference number.

Each road, street or highway must be labeled. Include secondary names or route numbers to identify the roadway. It may be necessary to identify direction of travel on divided or controlled access highways. Identify railroads, rivers and creeks or streams. Label any buildings depicted on the sketch. Residences can be identified by address and businesses by name.

Avoid labeling ejected occupants as driver and passenger because this is an opinion, not fact. Label signs by type or message. Often the face of the sign is drawn with an arrow pointing to its location. Other significant features should be labeled as desired. Try to position labels so that the diagram does not become cluttered. When needed, draw arrows from the label to the location of the feature described. The arrow should be drawn from the beginning or end of the label, never the middle and arrows should never cross each other.

Ensure that north is labeled on your sketch. This is typically indicated with a north arrow. North arrows are drawn in many styles. The only requisite is that it clearly shows which way is north. It is not necessary to label the three remaining directions.

AFTER-COLLISION SITUATION MAPS (SCALE DIAGRAM)

An after-collision situation map is a scale diagram of the results of the collision and roadway. Scale diagrams are not created for every collision you investigate. If no legal action arises from a collision, and no reconstruction is performed, a scale diagram is seldom needed. However, if a trial resulting from a collision is convened, a scale diagram is usually prepared as an exhibit. Additionally, scale diagrams are nearly always needed in crash reconstruction.

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Like the field sketch, the scale diagram should only contain factual data. Opinions or the findings of a reconstruction can be included on overlays or on a separate diagram. Tire marks, metal scars, and final rest positions of vehicles and bodies should be depicted on the diagram. Significant features such as parked vehicles, construction areas, and view obstructions should also be included and roadway and roadside improvements such as pavement edges, lane markings, traffic signs and signals, fixed objects, and sidewalks should be depicted. An after-collision situation map is more detailed and accurately drawn to scale than a field sketch.

After-collision situation maps are intended to be “true and accurate representation” of the collision site. If your measurements are wrong or if there are errors in reading or recording distances, the scale diagram will be inaccurate. Omitted measurements can also affect accuracy. It is extremely important to ensure accuracy on your field sketch and in taking measurements to help create an accurate scale diagram.

Typically, inadequate or missing data is the root of most problems. In many cases, no measurements were taken at the scene. The results quickly disappear and can only be reestablished through photographs when available. In some cases, poor measuring techniques were employed. Reference points are used which cannot be reestablished or the investigator may fail to follow any method for taking measurements. A typical error results when single measurements are made to one reference point. It is impossible to locate any point with only this data.

Templates Traffic crash templates are instruments that allow traffic crash investigators, engineers, architects, claim adjusters, lawyers, and other professionals to quickly prepare scale maps of traffic crashes, calculate speeds from skidding distances, estimate stopping and acceleration distances, change miles-per-hour to feet-per-second (metric model changes kilometers-per-hour to meters-per-second), measure angles and grades, and illustrate arrangement of parked vehicles. Made of transparent plastic, it also serves as a clinometer to measure road grades and super elevations when used with a slightly modified clipboard. Examples of two templates are shown in Figures 3-10 and 3-11.

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(Figure 3-10 Traffic Crash Template)

(Figure 3-11 Mini-Template)

Return the Scene to Normal (Normalize)

When responding to a crash scene, the first steps you take are protecting life and preserving evidence. You may have to divert traffic around the crash scene in nearby lanes or you may have to detour drivers to a totally different route after completely closing off the area to any passing traffic. One of the final steps at the scene is to clean up the crash site and return it to normal as soon as possible.

Delays in traffic due to crashes are frustrating for the public and can lead to more crashes. Drivers may be distracted by the crash or they may drive faster to make up for lost time after passing the crash scene. Behaviors like these can lead to additional collisions. Ensure you have the information you need to document the crash then return the scene to as normal as possible allowing traffic to flow as usual.

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SUMMARY

The at-scene investigation is the most important level of collision investigation. Inadequate or incomplete documentation of the results of the collision severely limits the extent to which a crash can be reconstructed. Follow-up investigators and reconstructionists depend upon the data collected by the at-scene investigator. Too often the at-scene investigator exhibits a lackadaisical attitude towards taking measurements and collecting other evidence at the scene. These investigators forget to take measurements or record them wrong or withhold sketches and scale diagrams from the report. You must fight this urge when you are at a scene where conditions are less than favorable. Follow-up investigators and reconstuctionists are at the mercy of your investigation if any follow up is required.

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Eleven – Step Summary

1. Decide what results of the accident to locate at the scene.

Position of each vehicle and any body outside of vehicle.

Scars (gouges and scratches) on the road, roadside, and fixed objects.

Debris areas: significant vehicle parts and pedestrian possessions; underbody dirt; vehicle junk; liquid spatter, dribble, and puddles.

Tire marks: skid marks, yaw marks, collision scrubs.

Parked vehicles which may have obstructed view.

Barricades and construction vehicles or materials.

2. Decide what spots must be located for each of the results.

One spot for debris areas and clusters of scars less than 3 feet long; bodies; detached vehicle parts; pedestrian possessions, irregularities and crossings of tire marks.

Two spots for each vehicular unit (trailers separate), skid marks, curved tire marks less than 6 ft. long, grooves or scrapes more than 3 ft. long.

Three or more spots for debris areas more than 3 ft. long and at regular intervals along yaw marks more than 8 ft. long.

3. Decide which system of measurements is best.

Coordinates with roadway edges as reference line.

Triangulation with permanent landmarks as reference points.

Combination of coordinates and triangulation.

4. Mark spots on the road and roadside.

RP’s for coordinates. Spots for vehicles or bodies which will be

removed before measurements are made. Faint beginning and end of tire marks

(erasure). Stations on reference line for long curved tire

marks. On perimeter of debris area. Others for convenience in referring to letter or

number designations.

5. Start field sketch.

Skeleton of roadway edges. Dotted line to indicate edges aligned on

opposite sides of intersection. Results of accident from Step 1. Spots to be located from Step 2.

6. Prepare table for recording basic measurements.

For coordinates three columnsSPOTS [N-S] [E-W]

For triangulation three columnsSPOTS [RP1] [RP2]

One horizontal line for each spot.

7. Make measurements and enter them in table.

To nearest half foot usually close enough.

Use decimal point for feet and tenths, underline inches, and spell out “steps.”

8. Decide what additional and supplementary measurements are needed.

Vertical measurements for edge of drop off; temporary view obstructions, such as vegetation and parked vehicles; fall distance at construction sites, roadway widths, distance between units, distance between RP’s.

9. Make the additional measurements.

Record where convenient on field sketch or by table of measurements.

10. Review field sketch and measurement records for clarity and completeness.

Make desirable additions and corrections.

11. Complete items of identification.

Sketch type (field or scale). Nominal north direction. Names of roads involved. Description of RP’s. If not at road junction, railroad crossing

or bridge, add distance and direction to some such recognizable landmark.

City and/or county and state. Time of day and date of crash. Name of person making measurements. Date of measurements actually made. Crash or case number for reference. Measured by (zero end & read end). Document &/or case number. Final positions & directions. Grade. Tire marks. Label units.

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WISCONSIN MOTOR VEHICLE ACCIDENT REPORT

OVERVIEW OF WISCONSIN ACCIDENT REPORTS (Document and Debrief)

Wisconsin Motor Vehicle Accident Report Form (MV4000)

Most officers do not use the majority of traffic and safety responsibility laws every day. You may feel it is not important to learn or understand them, however, if you feel this way, you are wrong. Officers have a professional responsibility to learn these things well enough that they can make correct decisions, give proper advice, and enforce the laws effectively.

You already learned what actions to take at a crash scene to stabilize the scene and collect evidence and measurements. The next step is documenting your findings. Again, rely on the steps you learned up to this point to collect information at the scene; do not rely on the Wisconsin Motor Vehicle Accident Report Form to dictate your actions at the scene. Traffic-collision reports are used to record routine data at a crash scene. An officer must complete a Wisconsin Motor Vehicle Accident Report (MV4000) when a crash originates or terminates on a traffic way, which involves at least one motor vehicle in transport, and results in any of the following:

1. Injury or fatality of a person.2. Total damage to one person’s property to an apparent extent of $1000 or

more.3. Damage to government-owned property to an apparent extent of $200 or

more, except government-owned vehicles, which are $1000.5

If a crash meets any of these three criteria, an MV4000 must be completed by the investigating agency. Filling out this form merely records specific data at the crash scene. It does not constitute a full investigation of the crash. Law enforcement officers must take other factors into consideration when investigating a crash. The MV4000 should only be considered as part of an investigation.

Law enforcement officers should use the Law Enforcement Officer’s Instruction Manual for Completing the Wisconsin Motor Vehicle Accident Report Form when completing an MV4000 form. This manual was developed to aid law enforcement officers with completing the scannable MV4000 form. Officers

5 Division of Motor Vehicles. 1998. Law Enforcement Officer’s Instruction Manual for Completing the Wisconsin Motor Vehicle Accident Report Form (MV4000). Page 2.

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should use a #2 Pencil when completing the scannable MV4000 form and ensure they fill the bubbles completely when asked to do so.

Information written on the form should be typed or printed in block-style, uppercase lettering. Officers should double check each field for errors prior to submitting the form. Reports submitted to the Traffic Accident Section at the Bureau of Driver Services, Division of Motor Vehicles will be returned to your agency if they need correcting.

Users of Traffic Crash Reports

Drivers Involved Owners of Property Struck by Drivers Involved DMV Traffic Accident Section DMV Uninsured Motorists Unit Courts District Attorneys Defense Attorneys Police Administration & Police Officers Local Government Decision-Makers Driver Educators Emergency Medical Services Personnel County Boards and City Councils National Highway Traffic Safety Administration Federal Highway Administration Traffic Crash Reconstruction Specialists County Traffic Safety Commissions Traffic, Maintenance, and Design Engineers DOT Bureau of Transportation Safety (BOTS) DOT Highway Safety Strategies Section State & Local Transportation Planners Insurance Companies DMV, i.e., points for traffic violations Media

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Figure 4-1 through 4-6 show examples of a completed MV4000 form and a MV4000 Supplement Form (Wisconsin DOT).

(Figure 4-1)

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(Figure 4-2)

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(Figure 4-3)

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(Figure 4-4)

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(Figure 4-5)

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(Figure 4-6)

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Driver Report of Accident Form (MV4002)

If a collision is considered a “reportable accident,” and a law enforcement agency does not investigate the accident, the operator of each motor vehicle is required to complete a Driver Report Accident Form (MV4002). Inform the operators that forms are available at police, sheriff’s departments, State Patrol districts, or Department of Motor Vehicle customer service centers.

(Figure 4-7 Driver Report of Accident MV4002 – Page 1)

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(Figure 4-8 Driver Report of Accident MV4002 – Page 2)

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Badger TraCS and the MV4000

Badger TraCS includes electronic report forms, including the Wisconsin Motor Vehicle Accident Report (MV4000), the abbreviated MV4000 for single unit, property damage vehicle/deer crashes, a form for amending previously submitted MV4000s, a Uniform Traffic Citation, an Alcohol Incident Reporting form, A uniform Municipal Citation, a Warning Citation, and an Attachment form to submit photos and other supplemental information. TraCS runs on both stand alone PCs and laptop computers in squad cars. This allows for immediate data entry in the squad car or entry at a later time at your agency. Driver/vehicle information can be replicated among forms, eliminating duplication of entry.

Reportable crashes can be submitted to the DMV/TAS electronically. Law enforcement is able to archive crash data on their servers and generate copies as necessary. The MV4000e contains all the fields on the MV4000 arranged in a different order. The amended crash form is the same as the MV4000e, with the addition of a Document Number Override field. This field contains the original document number that is amended. Figure 4-9 is an example of Badger TraCS.

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(Figure 4-9)

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DRIVER, VEHICLE, ROADWAY, AND ENVIRONMENTAL CONDITIONS AND FACTORS PRIOR TO THE COLLISION

Generally, information about the conditions prior to the collision are recorded on the MV4000 by indicating which category in each of several classifications best described the conditions of the driver, vehicle, roadway, and environment at the location of the collision. Conditions refer to the officer’s observations. Factors refer to the officers opinions. There are separate areas on the MV4000 for listing this information; however, officers must understand the difference between conditions and factors prior to completing the form.

Driver Condition

Driver condition data is based on your observations at the scene of the crash and/or based on the chemical test results made available during the investigation.

Presence of Alcohol or Drugs. For each operator or pedestrian involved in the crash, determine if there is a presence of alcohol or other drugs. You may have to get this information later if injured individuals were transported to a hospital.

Driver actions. For each driver, determine what the driver was doing at the time of the crash. For example, were they changing lanes, turning right at a red light, etc?

Pedestrian actions. When a pedestrian is involved determine the location of the pedestrian involved in the crash during the first harmful event. Also identify what actions the pedestrian took that may have been a factor in the crash. For example, did they disregard a signal, dart into the road, etc?

Roadway Conditions

Road Surface Condition. If conditions suggest that some road surface condition might have contributed, make a record of the actual conditions. Do not, at that time, try to decide whether the condition actually did contribute to the crash. The classification for road surface conditions is classified as: Dry, Wet, Snow/Slush, Ice, Sand/Mud/Dirt/Oil, Other, or Unknown. More detailed descriptions of road surface conditions that may lead to crashes are listed below.

Slipperiness: You should ask the question whether the slipperiness of the road surface either surprised the driver or prevented successful evasive tactics when the driver was confronted by a hazardous situation. Conditions that make pavement slippery include: moisture, ice and snow, loose gravel, leaves or grass – especially when wet, oil spots or grease,

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and asphalt or tar joints that are softened by hot weather. More often than not, investigators will find no tire marks when slippery surfaces do contribute to crashes. Do not let the lack of tire marks deter you from considering slipping as a contributing factor.

Ruts: Are deep wheel tracks in hard material, usually ice, but sometimes dirt. They contribute to crashes by interfering with normal control. Ruts are much more likely to be a factor at high driving speeds. Be sure to consider whether holes or ruts in the roadside or the shoulder were made by the vehicle as a result of the crash or were they there before.

Holes. Holes in the paving have to be a foot or more long and wider than a tire to be hazardous. Several small holes in a row can give enough of a rough ride to make a driver lose control where a single hole would not. When a tire hits a hole hard enough to be dangerous, you will sometimes find evidence of the blow on the tire. Such marks confirm, rather than prove, a conclusion regarding the hole as contributing to the crash.

Curbs. Curbs act like ruts. If a tire strikes one at an angle, you should find scuff marks on the outside of the tire and probably will find them on the curb. These marks often indicate where the vehicle went off the roadway. When a vehicle strikes a curb at an angle and then swings toward it so that both front and rear wheels strike, the wheel which strikes first will nearly always leave a much more prominent sign of scuffing, both on the tire and on the curb. This is because the first wheel strikes harder. In most cases of this kind there is also a contributing driver action.

A Lip or Drop-off. A lip drop-off is simply a low shoulder at the edge of hard pavement. It is more important when the shoulder is more than three inches below the pavement, especially on concrete paving with a vertical edge. Most crashes involving drop-offs occur when a driver tries to steer back on the pavement without slowing enough. The lip acts as a rut or rail, which keeps steering from being effective until the front wheels are turned at a fairly sharp angle. Crashes that result from a car dropping off the edge of the pavement are often detected by matching signs of it on the inside of the front right tire and on the pavement edge. The drop-off may occur a hundred feet or more before the point of collision.

Soft Shoulders. Soft shoulders can cause the driver to lose control at high speeds.

Braking while partly on the shoulder. If the brakes are applied strongly while the right wheels are on the shoulder and the left wheels are on the pavement it will create a much greater drag factor on the left than on the right. This difference in drag factors will cause the vehicle to rotate counterclockwise with the result that it heads back across the road. The

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sidewise sliding on the shoulder will cause the wheels to dig in and the vehicle may roll over. At speeds greater than 35 mph, especially if the brakes are released, the vehicle will suddenly go across the road to the left.

Traffic Control. If traffic control devices are present at the scene of the crash, you should record their condition and visibility for those drivers who are required to respond to them. These devices include signs, signals, pavement markings, speed limits, prohibited turns, one way streets, etc. Exactly what descriptive data are required depends on the circumstances of the crash. For example, there are some collisions in which the timing of the traffic signals is important and must be observed and recorded.6 This is especially important if you decide to initiate any enforcement action based on the driver failure to respond to them.

Environmental Conditions.7

Light Condition. The road or anything connected with it may be temporarily modified by conditions existing at the time of the collision. Light condition is usually classified according to three categories: Daylight, Dawn or Dusk, or Darkness.

Visibility/Weather Conditions. Visibility may change quickly so you must note it as soon as possible. Low visibility is usually created by darkness, fog, snow, falling rain, glare from the sun, or other atmospheric conditions. When visibility is low, objects gradually become visible as they loom up in the distance.

View Obstructions. Unlike objects that gradually appear due to reduced visibility, if the view of an object is obscured, the hazard appears rather suddenly from behind or from the back of a solid object. The best way to evaluate the view is to put yourself in the driver or pedestrian position. View obstructions on the road are usually vehicles, either moving or parked. They can prevent drivers from seeing signals, signs at the roadside, other vehicles, or pedestrians.

CONTRIBUTING CIRCUMSTANCES TO A CRASH

You will be asked to provide your opinion in three areas on the MV4000. Based on your observations and the information collected at the scene provide your opinion on any driver factors, vehicle factors, or highway factors that may have contributed to the crash.

Driver Factors 6 Baker, Kenneth, S. (2001) Traffic Collision Investigation. P. 1727 Baker, Kenneth, S. (2001) Traffic Collision Investigation. Pg. 172 - 173

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Observe each operator or pedestrian involved in the crash. Determine if the individuals appear to be normal, have reduced alertness, or are impaired. On the MV4000, fill in the bubble that best describes the driver or pedestrian’s appearance. There may be instances when you are not able to observe the driver’s condition, for example, during Hit & Runs, if the driver leaves the scene prior to your arrival, etc.

You will also offer your opinion about what the driver may have done to contribute to the crash. For example, from the information you gather, you may feel that the driver was exceeding the speed limit or driving too fast for conditions. Consider your observations and facts then formulate your opinion and document it on the MV4000.

Vehicle Factors

After inspecting the vehicles involved in the crash, determine if some sort of vehicle malfunction contributed to the crash. Examples might include, faulty brakes, a blown out tire, a burned out turn signal or failure of head lamps, etc. Again, this is your initial opinion about the vehicle based on your findings at the scene.

Highway

In your opinion, list any highway factors that may have contributed to the crash. These include factors like the highway being wet from snow or rain, or was there ice that one or more of the vehicles could have slid on. Were there any issues with the road itself, such as a narrow, low, or soft shoulder, loose gravel, rough pavement or debris in the road that caused the vehicle to swerve, etc? Fill in the appropriate highway factors that may have contributed to the crash in the appropriate block on the MV4000.

SUMMARY

The Traffic Accident Section (TAS) of the Wisconsin Department of Transportation receives the Wisconsin Motor Vehicle Accident Report (MV4000) from all law enforcement agencies. Periodically MV4000’s are returned to the reporting agency due to incomplete or inconsistent data. Correcting, returning, and following up on the MV4000 can be time consuming for all parties involved. Check for errors prior to submitting your reports. This will prevent the need to return crash reports and save time spent making corrections. Some of the top reasons for MV4000 returns are:

Injuries in field 7 do not match injuries in fields 38 and 70. Vehicle or owner information is missing.

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Power unit not listed for trailers legally parked along highways or roadways.

Incorrect date of birth or drivers license number. Illegally parked vehicles. Missing driver information for driverless motor vehicle crashes. Incorrect vehicle information. Dealer plate with owner listed as individual. Double deer hit. If two vehicles hit the same deer, vehicle information is

required for both vehicles. Drivers listed in the driver area who are under the age of 7.8

8 Wisconsin Department of Transportation, Traffic Accident Section. Crash Chronicle. Summer 2004.

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PHOTOGRAPHING THE SCENE

CRASH SCENE PHOTOGRAPHY

Crash scene photography is fundamental to the preservation, evaluation, interpretation and presentation of physical evidence. In many instances, photographs can describe objects better than words. Photographs are used in conjunction with measurements and well written reports to capture the results of a crash. A traffic crash photographer’s goals include producing accurate, detailed images that record the locations, conditions and reflect evidence as clearly and objectively as possible.

There is a wide variety of equipment and procedures available to law enforcement officers for the purpose of taking photographs. Your agency’s equipment may include either film or digital imaging and may produce still images or video images. Whatever media you use to capture images, officers can expect to be called upon in court to verify that the images/photographs accurately represent the scene and the event at the time of the photographer’s observations.

Use of Photos

People tend to believe that “photos do not lie.” Even though a photo might not be a completely “true representation,” it is regarded as relatively free from bias that my influence verbal or written reports. Photographs refresh the memory about something seen in the past and often make notes and observations unnecessary. A spare photo can be marked making the photo more effective in reminding you of what you observed. It is also useful to mark each photo of a collision scene with a small arrow to show which direction is north.

Misused Photos

Investigators can be led astray by the obvious advantages of photography in a collision investigation. Photographs should not be used as an easy way out of arduous observing and measuring. An investigator should think of photos only as a means of recording what he or she thinks is important. He or she should avoid taking pictures as a substitute for observations and not expect to find in a picture what he or she failed to note before making the picture.

Anyone who has ever tried to make a map from a photograph knows why photos are not adequate substitutes for measurements. It is true that by photogrammetry, maps can be made from photos, but this is a tedious and expensive process. Therefore, photos supplement but are not good substitutes

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for written notes, classification of damage, description of the collision location, measurements, and above all careful observations by the investigator.

Spare photographs may be marked as you please, but otherwise mark other photographs in only one of three ways:

On the back. With a soft “china-marking” crayon which can be cleaned off easily. On a transparent or translucent overlay, either tracing paper or acetate.

Photos marked with pens or felt-tipped markers are ruined for some purpose. Consider using a spare photograph or mark a copy made from a copy machine.

“AT SCENE” PHOTOS

Basic “At-Scene” Photos

The particular purpose of at-scene pictures is to show how the situation looked when vehicles came to a rest after the crash, how objects were arranged and how things were related to each other. These photos enable anyone interested to see quickly how pictures of specific details relate to the whole crash scene.

Following a preliminary evaluation of the scene, officers will be called upon to take scene photos in a series of overviews, mid-range views, and close-ups if necessary. Generally speaking, a photographer will have four overall views of a crash scene. These are usually taken from 150 feet or further from the crash scene. Then, medium views will cover the entire roadway width at or near the area of impact. Also, consider one photo to represent each driver’s/participant’s view as they approached. It is helpful to try to take these photos from the participant’s actual view. For example, a photo from 36 to 42 inches above ground level might reasonably simulate a driver’s perspective while seated behind the wheel of an average car. And lastly, consider the best overall picture of the scene. This single representation seeks to include all vehicles, all the results and some distinguishing landmark to help represent things in the best possible perspective.

To completely document a crash scene photographers should try to reflect what shows on the roadway. This includes skid marks, yaw marks, any other kind/s of tire marks, and both solid and liquid debris. The photographer’s goal is clearly to show what is there but in some cases it might be just as important that photos be used to document what is not present at the time of the investigation.

In Figure 5-1 position A gives a view straight down the road, includes both cars, some debris, and a landmark stop sign; the Ford obscures most of the Chevrolet and all tire marks. Position B is a good view of the right side damage of the Ford,

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but it does not show whether the vehicles are actually touching each other. The tire marks and stop sign are too far to be clearly visible. Position C is a good view of damage to the left side of the Chevrolet. It clearly shows that the cars are still engaged, but it omits the tire marks and both landmark stop signs. It does not show the position on the road well. Position D includes everything but is so far off (more than 80 ft) from anything significant to be very useful.

The angles included in these undesirable views are shown as dotted lines in Figure 5-1. Position E shows everything that Position D does, but better. It is close enough to show the tire marks well. It also shows major debris. Aimed straight down the middle of a lane, it shows the position of the vehicles on the road and indicates that they are engaged. This is the best overall picture.9

Baker, K. S. (2001) Traffic Collision Investigation, p. 264

CHEVROLET

FORD

.

STO

P

SKID DEBRIS

SCALE

20 30100

FA

B

CD

STO

P

.

E

(Figure 5-1)

Photographs can help identify the location of marks on the road. You can do so by:

Including a nearby landmark, or Capturing two images – one of the item of interest accompanied by one

which includes a background object that relates the item to the scene, or Including some kind of an identifying mark within the photograph.

For the purpose of documenting long marks, typically 40 feet or more in length, you should begin by photographing the start of the mark, the end of the mark, and any peculiarity in between. You should also consider photographing the 9 Baker, K.S. (2001) Traffic Collision Investigation, p. 263 – 264

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mark at regular intervals along it. And you should pay special attention to any changes in direction or peculiar areas in the texture of the road. For example if the road changes from concrete to asphalt you would pay special attention to that location where the tire mark switches from one to the other.

Photographing Vehicle Damage

Photos are a particularly useful way to document vehicle damage. In order to reconstruct the event and to evaluate cost to repair, these photographs are generally best done at the scene. Most crash investigation vehicle damage images can be documented in a standard record of four photos. Starting at the front of the vehicle align your photograph along the vehicle’s center line and begin with one photo of each side working clockwise and standing squarely along the end or side of the unit. You may align the camera by using undamaged parts to give your best possible perspective.

The four standard pictures of vehicle damage.

(Figure 5-2)

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On completion of these four photos (one of each side), consider taking the one or two photos that best reflect damage to a vehicle. Once you have your overview of general damage, consider details which might be documented in photos. Some details of damage may include:

Imprints of one vehicle on another Friction and or abrasion marks Damage to lamps Damage to loads Sources of injury to pedestrians or occupants Detailed damage to tires, wheels, and the underside of the unit.

If a particular location on the car has some area of interest or evidence, like a light bulb distortion or paint transfer, close ups need to be taken. To do this, three standard photographs will be needed. The first shot is of the overall side of the vehicle, the second shot is closer to the area of interest, and the third shot is then a close up of the item of interest. Depending on what the item is, you may want to repeat these steps placing a scale near the item.

Photographs should be taken that would include any vehicle defects such as bald or worn tires, dirty or cracked windshields, or any pre-crash damage that could have contributed to the crash. Also take photographs of any vehicle modifications or aftermarket items that are on the vehicle; especially those suspected of contributing to the crash or altered the original specifications of the vehicle.

Last but not least would be photographs showing any interior damage sustained during the collision. Occupant-to-vehicle impacts are very useful in establishing occupant pre-impact seating positions. It is for this reason that photographs showing interior damage or implements of injuries to passengers be captured through photography.

Procedures for Photographing a Crash Scene

There are a variety of specific photos and considerations that might assist you in an investigation. Remember, if you need to photograph a vehicle’s interior, make your exposure as if there were no daylight. When photographing during hours of darkness, most camera flash units are only effective for about a maximum of 12 feet and reflective surfaces may be difficult or impossible to distinguish with use of a flash. Similarly, use of a flash during daylight hours may reveal things in shadow, such as underneath a vehicle that would otherwise not be visible. You may find an assistant useful to help point out specific things such as vehicle identification number plates, matched areas of damage between different vehicles, or some other specific evidence being portrayed in the photo.

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Take un-scaled photographs first, then introduce your scale and take another photo of the same visual image. Chalk items before moving them and then photograph the area chalked again. When you remove an item of evidence, photographing the surface underneath the item may avoid questions later. Always be cognizant of visibility conditions and/or obstructions such as fog, traffic control devices, parked vehicles, signs, or window conditions which may have been relevant to the participants in the crash. Photographs may be able to help you document a victim’s location and injuries when appropriate. A given vehicle’s condition can be documented as it might relate to the contents, tire condition, or any other indication that the vehicle may have been unsafe prior to the incident.

When taking the photographs try to avoid dramatic shots. Those showing excessive amounts of blood and gore are seldom useable in court. Despite what can be seen on television or at the movies these days, some courts frown on graphic photographs that might prejudice the jury. There are times, however, when those photographs have a purpose and if your intent is to show a position or implement of injury they are of use and should be taken. It is a common practice to take photographs of fatal victims in their final rest position and after being removed from the vehicle for evidentiary and identification purposes.

Try to avoid shots containing emergency vehicles and equipment. Seldom is it useful and most often they block important features that need to be viewed, if nothing else to show relationships. A tire mark obscured by emergency vehicles may miss some important characteristics of that mark which might be needed to help identify it properly.

OTHER CONDITIONS DEALING WITH PHOTOGRAPHY

TIPS/Techniques

The following are techniques that you may find helpful to make your pictures more useful. The application of these techniques is dependent on what type of camera equipment you will be assigned or using.

The use of “fill flash” is a technique used to eliminate shadows when taking daytime photographs. Most cameras allow for this feature. By using the cameras flash during the day, it sends light into areas that normally would be shadowed or covered by the normal light. The areas that would show up on a normal picture dark now show detail. This works in areas where you have under-ride damage under a hood or bumper, on the underside of a vehicle, or in wheel well like when photographing the tread on a tire.

Avoid pointing your camera directly at shiny objects such as chrome or glass when using flash photography. If you must use a flash, the light should be cast

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from the side or at an angle. If you shoot the flash directly at the shiny object, you will get flashback, which burns out the detail of the object.

When taking photographs of glass and other transparent items such as instrument panels, consider the use of a polarizer. Polarizers reduce glare. Using a polarizer allows the ability to see detail behind the glass. Examples of this are when photographing a V.I.N. plate on a dash, hair or tissue on a windshield star, or speedometer or tachometer needle setting in a dash.

Another useful area for polarizers is for enhancing color contrast. Polarizers separate and contrast like colors. Examples of where this is useful is when locating and photographing tire marks or road scars on a roadway, or when you have paint transfer on colors that are very similar.

SUMMARY

As you can see by this chapter there is more to taking pictures then pointing at a subject and snapping the shutter. It is important you understand when to take photographs and what to take photographs of. Many different people use the photos you will be taking and they are just one of the steps in providing a complete professional investigation.

Your agency will provide you with additional guidelines and requirements that you will have to follow when taking pictures. You should read the owners manual for your particular equipment and become familiar with its operation. When you are at a crash scene and traffic is backed up or the weather is bad is not the time to be stumbling around in the use of your camera or other equipment.

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APPROPRIATE ENFORCEMENT ACTIONS

PROCEDURES TO DETERMINE SPEED ESTIMATES

Knowing the initial speed of a crashed vehicle can be of great value to the investigator in reconstructing what happened and why. Drivers may not admit or even know their actual speed at the time of the crash and many times the speed estimate of witnesses is unreliable. A scientific method which eliminates much of the guesswork is that of computing initial speeds from the measured length of skid marks left by tires sliding on the pavement.

The actual computation of speed from skid marks is a specialized skill involving the use of complex mathematical formulas and is beyond the scope of this text. The basic methods of computation, however, are outlined in Appendix B. This section covers the theory behind the computations and the methods of collecting evidence to be used in such calculations.

Excessive speed or driving at speeds too great for conditions is a common cause of crashes. When faced with an emergency, a driver will usually apply the brakes with maximum force. The driver may also swerve the vehicle sharply. The resulting skid marks provide evidence which can be used to compute, with reasonable accuracy, the initial speed of the vehicle. As long as your measurements are accurate, a reconstructionist will be able to estimate the vehicle’s speed prior to the crash.

ENFORCEMENT ACTIONS

As with any other incident you are dispatched to investigate as a law enforcement officer, traffic crashes may require you to take some form of enforcement action. After you have obtained all the facts, evidence and statements available to you, the enforcement action you take will be dictated by traffic law, department policy and common sense. It is important that you complete your investigation before making a decision regarding who is, or is not, at fault or if both parties are to blame for the crash. Do not jump to any conclusions or make any premature statements.

Commonly, issuing a traffic citation to the at fault driver prior to returning to your assigned patrol duties will be the enforcement action you take, if any at all. Department policy, a comprehensive knowledge of traffic law, and common sense will all be factors in your enforcement decision.

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Some crashes, such as OMVWI or crashes that result in injury, death, or substantial property damage may require additional investigation. Often these crashes will require you to complete a detailed report to be forwarded to the District Attorney (DA) pending review for criminal charges.

You will need to accurately document all the facts regarding a crash in order to prevail in court if your DA charges a driver for a criminal violation. Your report will impact criminal proceedings and any civil litigation. It is critical that you have conducted a thorough and detailed crash investigation. Criminal and civil cases may take several years to come to trial requiring you to depend on your reports to provide credible testimony.

The thoroughness of your report will reflect on you as the investigating officer. Your professional reputation is important. Be sure you gather all the facts and are fair to all parties involved or affected by the crash.

All conclusions and actions must be based on the facts, evidence, and statements you personally have gathered or know to be true. You are not the agent for the insurance companies. You are an impartial taker of the facts. Do a professional investigation as a law enforcement officer.

ENFORCEMENT DECISION

After you have gathered all the facts and information regarding a crash you will need to make a charging decision. You will essentially have four options.

OPTION #1: No Formal Enforcement Action

Examples of crashes that you may decide not to take enforcement action on would be:

A “slide off” in bad weather resulting in minimal damage, yet sufficient enough to be a reportable crash;

A reportable non-injury crash where a driver hit debris on the roadway during night time or other conditions of reduced visibility;

A reportable crash where conditions a normal driver would not be aware of existed;

Striking livestock that entered the roadway that would have been unavoidable by the driver;

A car vs. deer crash.

OPTION #2: Issue a Traffic Citation

If there is not serious injury or death, moderate property damage, no criminal law violation or other extenuating circumstances you might issue a Wisconsin

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Uniform Traffic Citation (WUTC / MC4016). Examples of crashes that you may decide to issue a WUTC would be:

Stop sign violation; Wrong way on one-way street; Excessive speed for road / traffic conditions; Inattentive driving (i.e.: falling asleep / cell phone use) OWI 1st offense OWI with passenger under 16 years of age; Absolute sobriety violations; Failure to report traffic crash.

OPTION #3: Criminal Violations

Serious crashes may require you to forward your completed investigation report and charging recommendation to the DA for review and determination whether criminal charges are issued. Generally crashes involving serious injuries, fatalities, extensive property damage or unusual circumstances will fall into this category.

These crash reports may require the assistance of a traffic crash reconstructionist, detectives or other specialists to complete. Examples of Criminal Violations are:

Homicide by intoxicated user of a motor vehicle; Injury by intoxicated use of a vehicle; Crash as a result of a pursuit; Criminal OWI violations.

Non-Contributing Violations

Violations for traffic law violations that may not have directly contributed to the crash should also be enforced. Although these violations may not have been a direct cause of a crash, they are violations and should be enforced.

Examples of these violations are:

OAR / OAS; Vehicle registration violations; Financial responsibility violations; GDL violations; Seatbelt violations; Child restraint violations; Open intoxicant or other alcohol violations.

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Generally, as a law enforcement officer you will have a great deal of discretion as to what enforcement action you will take at the scene of a crash. If there were factors that would make a reasonable person believe the crash was unavoidable you would probably be on solid grounds for issuing a traffic citation.

It is important that you do not prematurely form an opinion regarding who or what caused a traffic crash. It is equally important that you, as the law enforcement officer investigating a traffic crash, remain neutral and not make comments regarding the cause of a crash until you have gathered all the information available as they relate to the crash.

Hastily spoken words can make enforcement action more difficult if drivers, occupants or witnesses agree with your original comment that was based on a quick opinion rather than facts. If you were incorrect in your assumption you may have a difficult time if you are challenged in court by drivers or other persons who heard your erroneous comment based on a too quick assumption of what happened.

You need to determine what your intent is when you issue a written citation at a traffic crash as with any other type of traffic contact. Are you attempting to correct driving behavior or simply penalize a driver for a traffic violation? Your primary objective should be to correct bad driving habits or behavior. HIT-AND-RUN INVESTIGATIONS10

The first steps in most hit-and-run investigations are the same as those in the investigation of any collision. Get to the scene safely and quickly and handle emergency problems. If you know before reaching the scene that the collision may be a hit-and-run case, watch for vehicles coming from the direction of the collision. Note descriptions and registration numbers if possible. One of these may be the vehicle involved.

At the scene, try and locate the drivers as soon as possible. If a driver cannot be quickly located, consider the possibility of a hit-and-run. Lose no time in stating a search for the missing driver. Get the best description possible of the missing vehicle and occupants. These may eventually lead to the driver. Communicate available information to a police dispatcher who can broadcast the description in the area. As soon as all available information about the missing driver has been obtained, go ahead with other steps of the investigation at the scene.

Hit-and-run driving may be either a felony or a misdemeanor. In cases resulting in injury or death, it is a felony. It is a misdemeanor where only property damage is involved. In either case, the incident should be investigated just as any other crash, except that special hit-and-run procedures should be followed.

10 Schultz, D. and Hunt, D. (1998) Traffic Investigation and Enforcement. p. 217 – 222.

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The officer investigating the hit-and-run is really conducting two investigations in one – to determine the cause of the crash and to determine the identity of the driver who has left the scene. It is one type of crash in which it is readily apparent that a violation has already occurred – that of evasion of responsibility. The officer, however, must not lose site of the fact that leaving the scene is not a cause of the crash. The investigation must be thorough in order to uncover the cause of the crash as well as to locate the missing driver.

Time is important in hit-and-run investigations. The longer it takes to locate he driver, the more time he or she will have to repair any damage to the vehicle, destroy evidence, and establish an alibi. Therefore, the initially responding officer faced with a hit-and-run investigation should broadcast this information for the benefit of other police units as quickly as possible so that a wide search for the violator may be put into motion.

It is not uncommon for a drunk driver to flee the scene of a hit-and-run incident either in the vehicle or on foot. The motive here is to avoid being charged with driving under the influence. Unless the driver is located quickly, any tests done to indicate driving under the influence may not be useful or incriminating. It is also not uncommon for drivers of stolen vehicles or drivers involved in other crimes to flee the scene of a collision for obvious reasons.

You should then proceed to interview any witnesses in more detail and try to obtain more details about the suspected vehicle and/or driver. You should try to determine if the suspect stopped at any time and if so did he/she talk to anyone? Any new information should be reported to dispatch so other units involved in the search may be advised. You should be alert for the return of the responsible driver to the scene to mingle with the crowd to see how the investigation is progressing – even going so far as to follow the officer very closely. The inquisitive person who displays an unusual interest in the progress of the investigation might well be the driver involved who is attempting to discover how close the investigation is coming to making and identification.

In addition to these steps, process the scene as you would with any other collision. Document and measure the scene and complete the appropriate paperwork. Follow-up activity will include checking garages, wrecking establishments, service stations, and body shops, and putting them on alert for a wanted vehicle. Good hit-and-run investigation and reporting means digging a little deeper to obtain more facts. It is the small detail that might be easily overlooked which, if found and checked, will lead to the apprehension of the suspect.

SUMMARY

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You will respond to a number of traffic crashes during your career as an officer. The conditions when responding to a scene are usually stressful and unpleasant experiences for everyone involved, however, you have a responsibility to properly record all of the facts surrounding the crash. Often times, you are the only person who is not emotionally attached at the scene and are the one person everyone at the scene is looking to for direction. Using the RESPOND model will help you stabilize the scene and get help for any injured or get any other resources needed to help at the scene.

This text introduced you to the basic skills and steps to follow when responding to cash scenes and investigating crashes. You learned the basic at-scene investigation techniques, including how to properly measure and document the scene. The accuracy with which you measure and document the scene will directly affect any advanced investigations or reconstruction so it is important that you take your time and follow the processes outlined in this text when measuring and documenting a scene and when completing the Wisconsin Motor Vehicle Accident Report (MV4000).

You did not learn any advanced techniques or reconstruction techniques. This level of investigation takes more training and experience. That does not mean the skills you learned are any less important, however. Any follow on investigations rely heavily on the work you complete at the scene. It is important for you to take your time and document the scene accurately. This text only introduced you to the basics; if you find yourself on a major scene you should follow your department policy and consider requesting help from a more experienced investigator.

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APPENDIX A - GLOSSARY

ACCELERATION – The time rate of change of velocity; change of velocity divided by time; a vector quantity measured in feet or meters per second per second or expressed as a decimal fraction of acceleration of gravity. Positive acceleration increases the velocity of a body, negative acceleration (deceleration) reduces the velocity of a body.

ACCELERATION SCUFF – A scuffmark made when sufficient power is supplied to the driving wheels to make at least one of them spin on the road surface.

ACUTE ANGLE – An angle that is less than a right, 90-degree, angle.

AFTER-COLLISION SITUATION MAP – A scale drawing of the scene after a traffic collision situation has stabilized; a geographical summary of results of a collision without indication of any assumed events of the collision or other inferential elements.

ANGLE COLLISION – A collision between two traffic units approaching on separate roadways or other paths that intersect.

APEX – The point at which two sides of an angle meet or cross.

ARC – A part of a curve, especially part of a circle, between two points on the curve.

AT-SCENE INQUIRY – Questioning informants at the scene of a traffic collision for the purpose of obtaining facts required for the official collision report and such other information as may be readily available.

AT-SCENE INVESTIGATION – Examining and recording results of the collision and obtaining additional information at the scene of a traffic collision which may not be available later and which supplements data obtained for the collision report. The information obtained is as factual as possible.

ATTRIBUTE – Any inherent characteristic of a road, a vehicle, or a person that affects the probability of a traffic collision.

BALLAST – Selected material placed on the roadbed to hold track in line. Ballast preferably consists of hard particles easily handled in tamping, which distribute the load, drain well, and resist plant growth.

BITUMINOUS CONCRETE – Concrete cemented with a bituminous material such as tar or asphalt.

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BODY TYPE – The general configuration or shape of a vehicle distinguished by characteristics such as number of doors, seats, or windows, roof line, hardtop, convertible, etc.

BRAKING DISTANCE – The distance through which brakes are applied to slow a vehicle; the shortest distance in which a particular vehicle can be stopped by braking from a specified speed on a particular surface; the distance from application of brakes to collision.

BRAKING TIME – The time required to traverse the braking distance.

CAUSE ANALYSIS – The effort to determine, from whatever information is available, including results of collision reconstruction, why the collision occurred, that is, the complete combination of circumstances that caused the highway transportation system to break down at the time and place of the collision. Cause analysis has been referred to as determining “indirect” or “condition” causes.

CENTERED FORCE – A force directed toward the center of mass of the vehicle or other object in a collision.

CHIP – A short, deep gouge; a hole in the pavement made by a strong, sharp, pointed metal object under great pressure, usually without striations.

CHOP – A broad, shallow gouge, even and regular on the deeper side and terminating in scratches and striations on the opposite, shallower side; a depression in pavement made by a strong, sharp metal edge moving sideways under heavy pressure.

CHORD – A straight line connecting the ends of an arch or two points on a curve. A chord is never greater than the diameter of a circle of which the arc is part.

COEFFICIENT OF FRICTION - The drag factor created by a surface causing a body sliding across it to slow it down; represented by a number, usually a decimal less than 1.00; and used in calculating speed from skid marks.

COLLISION RECONSTRUCTION – The effort to determine, from whatever information is available, how the collision happened. Reconstruction was formally referred to as determining “behavioral” or “mediate” causes of a collision.

COLLISION SCRUB – A short, usually broad, skid mark or yaw mark made during engagement of the vehicles in a collision.

CONCRETE – A paving material consisting of an aggregate of stones of assorted sizes held together with a cement binder; bituminous concrete, Portland cement concrete.

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CONTACT DAMAGE – Deformation or defacement resulting from direct pressure of another object or surface in an impact, direct damage. Compare with induced damage.

COORDINATE MEASUREMENTS – A method of locating any spot in an area by two measurements from the nearest point to the spot on a specified reference line; 1) the distance and direction from that point to the spot, and 2) the distance and direction from that point to a specified reference point on the reference line.

CRASH – The collision of a vehicle with another vehicle, a person, a fixed object, or a vehicle rollover.

CRASH INVESTIGATION – The systematic collection of evidence, the examination of information, and the recording of data to identify crash factors.

CRASH REPORTING – The standardized method of recording crash data derived from a crash investigation.

CRASH SCENE SPECIALIST – An officer who has been provided advanced training to conduct supplementary investigations of serious crashes, to gather data and evidence in more depth than the on-scene investigator, and to follow up on unresolved issues.

CROOK – An abrupt change of direction of tire mark due to collision forces. The crook often indicates the position of a tire at first contact.

DEBRIS – Loose material scattered about at the scene as a result of a traffic collision; dirt, liquids, vehicle parts, cargo, personal belongings and other things.

DISCRIMINATIVE REACTION – A reaction to perception of an unfamiliar hazard or other situation which requires additional information than that immediately available to make a decision or which presents several choices of possible evasive tactics.

DRAG FACTOR – A number representing the acceleration or deceleration of a vehicle or other body as a decimal fraction of the acceleration of gravity; the horizontal force needed to produce acceleration in the same direction divided by the weight of the body to which the force is applied. When a vehicle slides with all wheels locked, on a level surface, the coefficient of friction and the drag factor have the same value.

DRIBBLE – Liquid debris from a vehicle or its cargo that drops to the ground, often leaving a trail, if the vehicle is moving, from a spatter area to a puddle.

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DROP OFF – The edge of pavement where it is more than about 2 in (about 5 cm) higher than the abutting shoulder.

ECCENTRIC FORCE – A force which is not toward the center of mass of the vehicle or the center of mass of the other object in a collision.

EDGE LINE – A line which indicates the edge of the roadway.

EXTRICATION – The removal of a victim trapped in a motor vehicle or in a dangerous situation.

FALL – A downward and onward movement in the air under the force of gravity after forward momentum carries an object beyond its supporting surface. Rotation during a fall is gradual and the object usually lands right side up.

FIELD SKETCH – A freehand map of the scene or site of a collision showing certain features of the collision or road configuration, usually for the purpose of recording measurements.

FINAL POSITION – The exact location of a vehicle or body after a traffic collision.

FIRST CONTACT POINT (FCP) – The exact point on a vehicle, pedestrian, or other objected touched in a collision or the place on the road or ground closest to the first contact between colliding objects. Sometimes called point of impact or collision point.

FIRST HARMFUL EVENT – The first occurrence of injury or damage.

FLAT-TIRE MARK – A scuffmark made by an overdeflected tire; a mark made by a tire which is under inflated or overloaded.

FLIP – A sudden upward and onward movement off the ground when an object’s horizontal movement is obstructed below its center of mass by an obstacle on the surface supporting the object.

FRICTION MARK – A tire mark made when a slipping or sliding tire rubs the road or other surface.

FULL IMPACT – An impact during which motion momentarily ceases between some area of the colliding objects while they are in contact with each other. If the colliding objects do not separate after the collision, the impact is complete.

GAP SKID – A braking skid mark which is interrupted by release and re-application of brakes or which terminates by release of brakes before a collision.

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GORE – The area immediately behind the bifurcation of two roadways, bounded by the edges of those roadways; the angle between two roadways where one roadway divides into two.

GOUGE – A pavement scar deep enough to be easily felt with the fingers; chip, chop, or groove.

GRADE – The change in elevation in unit distance in a specified direction along the center line of a roadway or the path of a vehicle; the difference in level of two points divided by the level distance between the points. Grades are designated in feet (meters) of rise or fall per foot (meter) of level distance or in rise or fall as a percent of the level distance. Grade is positive (+) if the surface rises in the specified direction and negative (-) if it falls in that direction.

GROOVE – A long, narrow, pavement gouge; a channel in the pavement made by a small, strong, metal part being forced some distance along the surface while under great pressure.

HATCHING – Shading consisting of closely spaced parallel lines in a drawing.

HAZARDOUS MATERIAL (HAZMAT) – Any chemical substance or material that can pose a threat to health, safety, and property.

HAZARDOUS MATERIAL INCIDENT – Any situation that deals with the unplanned release of hazardous material.

HIGHWAY - All public ways and thoroughfares and bridges on the same. It includes the entire width between the boundary lines of every way open to the use of the public as a matter of right for the purposes of vehicular travel. It includes those roads or driveways in the state, county or municipal parks and in state forests which have been opened to the use of the public for the purpose of vehicular travel and roads or driveways upon the grounds of public schools, as defined in s. 115.01 (1), and institutions under the jurisdiction of the county board of supervisors, but does not include private roads or driveways as defined in sub. (46).

HIGHWAY INCIDENT - Any event that disrupts the normal flow of traffic.

HYDROPLANING – Skidding on water. Tires ride on water film.

IDENTIFICATION – Designation of a road location, a vehicle, a person, or a traffic collision in such a manner as to positively distinguish it from all others of the same description. Identification is often accomplished by a unique number such as a vehicle identification number, registration number, or a driver’s license number.

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IDENTIFYING NUMBERS – Numbers and letters, if any, on a vehicle designated by the Department of Transportation for the purpose of identifying the vehicles; VIN is not the registration number.

IMPACT – The striking of one body against another; a collision of a vehicle with another vehicle, a pedestrian, or some other object.

IMPRINT – A mark on a road or other surface made without sliding by a rolling tire or a person’s foot. An imprint usually shows the pattern of the tire tread or shoe that made it.

INCIDENT COMMAND SYSTEM (ICS) – A system used to manage resources, such as personnel, equipment, and supplies, at the scene of an emergency.

INCIDENT COMMANDER – The person in the incident command system ultimately responsible for managing and directing an emergency response.

INDUCED DAMAGE – Damage to a vehicle other than contact damage. Often indicated by crumpling, distortion, bending, and breaking. Induced damage includes damage done by another part of the same vehicle. Compare with contact damage.

INFORMANT – Any person who communicates information.

INFORMATION – Any knowledge received concerning a particular matter, such as a traffic collision, from any source, regardless of the reliability of the knowledge.

INTENDED COURSE – The path that would have been followed by a traffic unit as a normal part of its trip had the situation hazard not led to evasive tactics or collision.

INTERCHANGE – A system of interconnecting roadways in conjunction with one or more grade separations, providing for the movement of traffic between two or more roadways on different levels.

INTERSECT – The point at which two straight lines, such as the extensions of two roadway edges, cross each other; the apex of the angle formed by two straight lines which cross. Also called point of intersection.

INTERSECTION – The area embraced within the prolongation or connection of the lateral curb lines, or, if none, then the lateral boundary lines of the roadways of two highways which join one another at, or approximately at, right angles, or the area within which vehicles traveling upon different highways joining at any other angle may come in conflict. Where a highway includes two roadways 30 feet or more apart, then every crossing of each roadway of such divided highway

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shall be regarded as a separate intersection. In the event such interesting highway also includes two roadways 30 feet or more apart, then every crossing of two roadways of such highways shall be regarded as a separate intersection.

JUNCTION – The general area where two or more highways join or cross within which are included the roadway and roadside facilities for traffic movements in the area. A junction may include several intersections of roadways.

LAST CONTACT – The final touching of objects in a collision before separation; the time and place on a traffic unit or traffic-way where this touching occurs. If colliding objects do not separate, there is no last contact.

LIQUID DEBRIS – Scattered liquids from a vehicle or its cargo; spatter, dribble, puddle, runoff and soak-in.

MAXIMUM ENGAGEMENT – Greatest penetration of one body, such as a vehicle, by another during a collision; instant of greatest force between colliding objects; time and place of this occurrence; position of bodies with respect to each other at this instant.

MECHANISM OF INJURY – The force or energy that causes traumatic injury.

MIDDLE ORDINATE – The perpendicular distance between an arc and is chord at the middle of the chord.

NOMOGRAPH – A chart on which three or more scales are arranged so that a straight line drawn through values on any two will cross the third at a corresponding value; a graphic calculator.

OBTUSE ANGLE - An angle greater than 90° and less than 180°.

ON-SCENE INVESTIGATOR – The first responding officer to a traffic crash who has been trained to preserve crucial evidence, to measure and photograph the scene, to interview drivers and witnesses, to take enforcement action, and to file reports.

OPPOSITE-DIRECTION COLLISION – A collision between two traffic units moving in opposite directions on the same roadway. Sometimes called a head-on-collision.

OVERDEFLECTED – A condition of a tire in which the pressure on the road is grater at the edges of the tread than in the middle; an overloaded or under inflated tire condition.

OVERREACTION – A driver’s excessive reaction to a hazardous situation that produces another, or additional, hazard. Overreaction is usually a matter of too

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much steering at high speeds, and often results in a yaw.

OVERSTEER – A characteristic of a motor vehicle as loaded that results in a tendency to swerve toward the inside of a curve, especially at high speed. Motor vehicles with more weight on the rear wheels than on the front, and with too little pressure in the rear tires are likely to oversteer.

PARTIAL IMPACT – An impact in which motion is continuous between the parts of colliding objects which are in contact with each other; sideswipe.

PASSIVE DEVICES – Non-electronic traffic control devices, including signs, markings, and other devices located at or in advance of crossing to indicate the presence of a crossing.

PERCEPTION – The general process of detecting some object or situation and comprehending its significance.

PERSPECTIVE GRID – A parallelogram of known size placed on a flat surface so as to appear in a photograph as a basis for locating marks or points which also show in the photograph of the surface.

PHOTOGRAMMETRY – The use of photographs in making maps.

PUDDLE – A wet area on the road or roadside where dribble accumulates after a vehicle has come to rest. A puddle often marks the final position of a vehicle after a collision.

REACTION – A person’s voluntary or involuntary response to a hazard or other situation that has been perceived; the response to a sensory stimulus. Reactions may be reflex, simple, complex, or discriminatory.

REACTION DISTANCE – The distance moved or traveled by a vehicle or other traffic unit during reaction time.

REACTION TIME – The time required from perception to the start of vehicle control for tactical or strategic operations.

REFERENCE LINE – A line, often the edge of a roadway, from which measurements are made to locate spots, especially spots along a roadway.

REFERENCE POINT – A point from which measurements are made to locate spots in an area; sometimes the intersect of two reference lines; RP. A reference point is described in terms of its relation to permanent landmarks.

REPORTING – Basic data collection to identify and classify a motor vehicle traffic collision and the persons, property, and planned movements involved.

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Only strictly factual information is wanted, no opinions.

ROAD – The part of a traffic-way which includes both the roadway, which is the traveled part, and any shoulder alongside the roadway. Where there are unmountable curbs, the road and roadway are the same. If there is a guardrail, the road is considered to extend to the guardrail.

ROADWAY – The part of the road intended for vehicle travel. It does not include paved or otherwise improved shoulders or what is sometimes called a berm or breakdown lane.

RUN-OFF – Rivulets of liquid debris from a puddle area flowing downhill toward soak-in at the edge of the pavement; frequently the source of tire prints after a collision.

RUT – A depression in soft or loose material, such as snow or dirt, made by a rolling tire.

SCAR – Any sign that the road, roadside, or fixed object has been damaged or marred by a traffic collision.

SCENE – The location of a traffic collision while people and vehicles involved are still there. Compare with site.

SCRAPE – A broad area of a hard surface covered with may scratches or striations made by a sliding metal part without great pressure.

SCRATCH – A light and usually irregular scar made on a hard surface, such as paving, by a sliding metal part without great pressure.

SCUFFMARK – A tire friction mark made by a tire that is both rotating and slipping on a road or other surface.

SHOULDER – That portion of the road contiguous with the roadway for accommodation of stopped vehicles, for emergency use, and for lateral support of the roadway structure; bank. The line between the roadway and the shoulder may be a painted edge line, a change in surface color or material, or a curb.

SIDEWALK – That portion of a street between the curb lines, or the lateral edge lines of a roadway, and the adjacent property lines, intended for use by a pedestrian.

SIMPLE REACTION – A preplanned reaction to an expected hazard or other stimulus.

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SITE – The location of a traffic collision after vehicles and people involved have gone. Compare with scene.

SITUATION HAZARD – A circumstance that more or less endangers a traffic unit on a trip and which must be avoided to prevent a collision.

SKIDMARK – A friction mark on a pavement made by a tire that is sliding without rotation.

SKIP SKID – A braking skid mark interrupted at frequent intervals; the skid mark made by a bouncing wheel on which brakes keep the wheel from turning. Compare with gap skid.

SLAVE FLASH – A supplementary photoflash placed at a distance from the master flash to increase the illuminated field in a photograph and fired by a photoelectric device actuated by light from the master flash.

SLOPE – Ground that has a natural incline, as the side of a hill. Inclination or slant, especially downward or upward.

SOAK-IN – An area on the shoulder or roadside saturated with liquid debris either at the end of run-off or as a puddle marking the rest position of a vehicle after a collision.

SPATTER – The collection of marks on the road made by liquid from the vehicle or its cargo squirted from containers on the vehicle by force or collision. Spatter areas are irregular in shape and often consist of many spots.

STABLIZED COLLISION SITUATION – The condition prevailing after motion and other action constituting the events of a collision have ceased and no further harm will ensue unless a new series of events is initiated by some means.

START (Simple Triage and Rapid Treatment) system – A system used at the scene of multiple casualty incidents to quickly assess and prioritize care according to three conditions: breathing, circulation, and level of consciousness.

STRIATIONS – Narrow, light, parallel stripes or streaks usually made by friction or abrasion on the roadway or on vehicle parts.

SUPEREVLEVATION – The degree to which the outside edge of a roadway is higher than the inside edge at a specific point on a curve; the changes in elevation per unit distance across the roadway from inside to outside edge; bank.

SWERVE – A slight deviation from a straight-ahead path.

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TACTIC – Actions taken by a traffic unit to avoid a hazardous situation; steering, braking, accelerating, etc. to avoid a collision or other collision. Often called evasive action.

TANGENT – A line that touches a curve at only one point and is perpendicular to the radius at that point; a term used to describe a straight offset method.

TECHNICAL FOLLOW-UP – Collection of additional facts from any source and organization and preliminary study of all available data relating to a collision.

TIRE FRICTION MARK – A tire mark made when a slipping or sliding tire rubs the road or other surface; skid marks; yaw marks; acceleration scuffs and flat-tire marks.

TIRE MARK – A mark made on a road or other surface by a tire on a vehicle; tire friction mark, imprint.

TRACKWIDTH – The distance on the ground between the center of the tire tread on one side of the vehicle to the center of the tire tread on the opposite side.

TRACKING – Marks made when tires roll through puddles, run-off, or spatter and, becoming wet, leave tire prints on the pavement as they roll on.

TRAFFIC – Pedestrians, ridden or herded animals, vehicles, street cars, and other conveyances either singly or together while using any highway for purposes of travel.

TRAFFIC CRASH RECONSTRUCTIONIST – An individual who has been trained to conduct an in-depth reconstruction of the causes, events, and results of vehicle crashes, including computation of speeds, direction of travel, and angle of collision on the basis of evidence collected by on-scene investigators and crash scene specialists.

TRAFFIC UNIT – An element of traffic; a person using a traffic-way for travel or transportation; vehicle; pedal cycle, pedestrian, etc.

TREAD – That part of a tire designed to come in contact with the ground.

TRIANGULATION – A method of locating a spot in an area by measurements from two or more reference points, the locations of which are identified for future reference. Compare with coordinates.

UNCONTROLLED FINAL POSITION – A final position reached by a traffic unit after a collision without conscious human intervention.

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UNDERBODY DEBRIS – Debris consisting of mud, dust, rust, paint, snow, o road tar loosened by collision from the underside of the vehicle body, fenders, and other parts.

UNIFORM VEHICLE CODE – A specimen set of motor vehicle laws, designed and advanced as a comprehensive guide or standard for state motor vehicle and traffic laws.

VEHICLE IDENTIFICATION NUMBER (VIN) – The number assigned to the vehicle by the manufacturer primarily for identification and registration purposes.

WHEEL BASE – The distance from the center of the front wheels to the center of the rear wheels or, if there is a tandem axle, the distance to the midpoint between the two tandem axles.

WITNESS – Any person other than a driver or passenger who was at the scene of a collision while vehicles or people involved were still there.

YAW – A sideways movement of a vehicle in turning; movement of a vehicle in another direction than that in which it is headed; sideways motion produced when sideways inertia force exceeds traction force. Often the result of overreaction or exceeding the critical speed. Sometimes revealed by tire marks on the roadway.

YAWMARK – A scuffmark made while a vehicle is yawing; the mark made on the road by a rotating tire which is slipping in a direction parallel to the axle of the wheel.

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APPENDIX B - Wisconsin 2008 Traffic Crash Figures11

587 persons were killed in Wisconsin motor vehicle traffic crashes. This is an average of two lives lost each day on Wisconsin traffic arteries.

46,637 persons were injured in 33,766 reported injury crashes and 542 fatal crashes.

Of the 587 persons killed, 10% (52 pedestrians and 9 bicyclists) were not drivers or passengers of motor vehicles. Fifteen percent (87) were motorcycle drivers or motorcycle passengers.

Of the 587 persons killed, 40% (234) died in alcohol-related crashes and 32% (187) died in speed-related crashes.

Fifty-six percent of all crashes occurred off the state highway and interstate systems, on county trunk highways and local roads.

The total number of registered vehicles was 5,455,985.

The total number of licensed drivers was 4,075,764.

The fatality rate per 100 million miles of travel was 1.29, up from 1.24 in 2007.

The 2008 Department of Transportation Field Observation Study on Seat Belt use states that in July, 2008, 74.2% of passenger vehicle occupants (front outboard) used their safety belts. (Front outboard refers to the driver and the right front seat passenger.)12

11 Wisconsin Department of Transportation 2008 Wisconsin Traffic Crash Facts

12 Wisconsin Department of Transportation Field Observation of Safety Belt Use in Wisconsin (July 2008) http://www.dot.wisconsin.gov/safety/motorist/crashfacts/docs/seatbeltuse.pdf

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Wisconsin’s Highway Safety Clock13

APPENDIX C – SLIDE-TO-STOP SPEED ESTIMATES13 Wisconsin Department of Transportation 2006 Wisconsin Traffic Crash Facts

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The formula used in calculating speed from skid marks is in which S

represents the skid distance in feet, V the speed in miles per hour, and f the coefficient of friction. This formula may be rewritten without changing its value as follows: V2 = 30 x S x f. What the investigator is concerned with is the speed. Simply substitute known factors in the right hand side of the equation, perform the multiplications, extract the square root, and you will get the minimum speed. This can be very easily done in a matter of a few seconds at the crash scene, which gives you a result close enough to guide you in the investigation. It is a quick method of determining whether there was sufficient speed involved to warrant further analysis.

Example:

An investigator measures 50 feet of skid marks on dry, level concrete. The driver involved states he was going only 25 miles per hour. The quick method of estimating initial minimum speed is V2 = 30 x 50 x 60, or 900. The square root of 900 is 30. Therefore, the minimum speed is 30 miles per hour. This can be done very simply without a test skid by arbitrarily assessing a 60 percent coefficient of friction.

The coefficient of friction can be determined a number of ways:

Test-skid the crash vehicle or a similar vehicle. Slide a test tire (not the whole vehicle) to get a friction coefficient. Use existing highway department skid numbers for the road in question. Look up the friction coefficient in a table and apply the appropriate

adjustments to them for the case at hand.

The first three methods are used in advanced investigations or in reconstruction. The last method may also be used in advanced investigations or in reconstruction. You can also use the table to estimate the speed at the scene. However, this will only give you an estimate. Enforcement action should not be taken based on your estimates.

The table of coefficients of friction gives a range of friction coefficients for several surface descriptions. The values given in the table are for passenger cars and pickup trucks equipped with typical tires. They are not typical values seen for heavy trucks. This table provides an average coefficient of friction figure for a car or pickup truck on a flat, straight surface. This table is reproduced from the Traffic Accident Reconstruction Manual, published by the Northwestern University Center for Public Safety. See page 62-14.

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V2

S=30f

105

While you will be able to reasonably calculate initial speeds by using this formula, presentation in court will probably require expert testimony, including explanation of the various physical laws and mathematical formulas involved. The expert, for example a reconstructionist, will rely on the information you give him from the at-scene investigation to reach his conclusion. This information must be accurate, understandable, and complete, for without this information skid-mark evidence will be of little value. With proper measuring and recording of skid-mark evidence, accurate minimum initial speeds can be computed.

In complicated cases where not all wheels slide, or where the skid marks are on different types of surfaces, it will probably be up to the expert to determine if any use can be made of the skid mark evidence. In these instances, however, it is important to record the evidence so that the expert may decide to what extent it is usable.

COEFFICIENTS OF FRICTION OF VARIOUS ROADWAY SURFACES

PORTLAND CEMENTNew, Sharp .80 1.20 .70 1.00 .50 .80 .40 .75Traveled .60 .80 .60 .75 .45 .70 .45 .65Traffic Polished .55 .75 .50 .65 .45 .65 .45 .60

ASPHALT or TARNew, Sharp .80 1.20 .65 1.00 .50 .80 .45 .75Traveled .60 .80 .55 .70 .45 .70 .40 .65Traffic Polished .55 .75 .45 .65 .45 .65 .40 .60Excess Tar .50 .60 .35 .60 .30 .60 .25 .55

GRAVELPacked, Oiled .55 .85 .50 .80 .40 .80 .40 .60Loose .40 .70 .40 .70 .45 .75 .45 .75

CINDERSPacked .50 .70 .50 .70 .65 .75 .65 .75

ROCKCrushed .55 .75 .55 .75 .55 .75 .55 .75

ICESmooth .10 .25 .07 .20 .05 .10 .05 .10

SNOWPacked .30 .55 .35 .55 .30 .60 .30 .60Loose .10 .25 .10 .20 .30 .60 .30 .60

DRY WET

Less than More than Less than More than 30 mph 30 mph 30 mph 30 mph

From To From To From To From To

DESCRIPTIONOF

ROAD SURFACE

Fricke, L. (1990) Traffic Accident Reconstruction. Northwestern University Center for Public Safety. p. 62-14.

(Figure B-1: This table lists coefficients of friction of various roadway surfaces. This table is not intended for large, heavy trucks.)

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REFERENCES

Daecher Consulting Group Inc. (n.d.) Accident Investigation: Getting Facts to Make Decisions. Retrieved August 31, 2007, from http://www.uma.org/ppt/AccidentInvestigation.ppt

NHTSA- National Center for Statistics and Analysis: Traffic Safety Facts; 2006

Wisconsin Department of Transportation, 2008 Wisconsin Traffic Crash Facts; June 2009 retrieved June 28, 2009 from http://www.dot.wisconsin.gov/drivers/drivers/traffic/crast/final.htm

Baker, J. Stannard and Fricke, Lynn B. The Traffic Accident Investigation Manual, Ninth Edition 1986

Fricke, L. (1990) Traffic Accident Reconstruction. (First ed.) Northwestern University Traffic Institute Center for Public Safety.

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