SKIDDING ACCIDENT SYSTEMS MODEL

By

Kenneth D. Hankins

R. T. Gregory

and

Wm. J. Berger

Research Report Number 135-1

Definition of Relative Importance of Factors

Affecting Vehicle Skids

Research Study Number 1-8-70-135

Sponsored by

THE TEXAS HIGHWAY DEPARTMENT

in cooperation with

The U. S. Department of Transportation

Federal Highway Administration

March 1971

TEXAS TRANSPORTATION INSTITUTE

Texas A&M University

College Station, Texas

Technical Reports Center Texas Transportation Institute

ACKNOwLEDGMENTS

This research was conducted under an interagency contract between

the Texas Transportation Institute and the Texas Highway Deparbnent. It

was sponsored jointly by the Texas Highway Department and the Federal

Highway Administration. Liaison was maintained through Mr. Kenneth D.

Hankins, contact representative for the Texas Highway Department, and

through Mr. Edward V. Kristaponis of the Federal Highway Administration.

Source material was furnished for various portions of the systems

model by Dr. Robert A. Clark, Dr. Donald L. Woods, and Dr. Richard B.

Konzen. The technique and methodology were reviewed by Dr. Larry J.

Ringer, and Dr. Robert E. Schiller, Jr.

DISCLAIMER

The opinions, findings and conclusions expressed in this publication

are those of the authors and not necessarily those of the Federal Highway

Administration.

ii

ABSTRAGT

The theory introduced in this report is intended to identify the

interdependence of factors influencing the skidding accident. The theory

proposes that an analysis of accident variables can be made through the

selection and quantification of the variables outlined in a Systems MOdel.

The selection and quantification then enables corrective measures to be

identified and evaluated.

iii

SUMMARY

The objective of this study has been the development of a Systems

Model to characterize the factors effecting wet-weather skidding. The

model identifies and classifies the more significant elements in a skid­

ding incident with particular emphasis given to the highway elements.

The model allows each element to be viewed with respect to the total

environment and hopefully will lead to a better analysis of specific

problem areas in order to correctly formulate effective corrective pro­

cedures.

iv

IMPLEMENTATION STATEMENT

The Systems Model provides the engineer in the field a useful guide

which points out many important factors which can contribute to skidding

accidents. By illustrating these factors for the engineers' considera­

tion, a variety of potential solutions may be indicated. Future and

current work will be and is devoted to quantifying the effects of many

of these factors. The Systems Model is necessary for the proper organi­

zation of this work. The model allows each element to be viewed with

respect to the total accident picture. Ultimately the model may be used

as a guide in re-evaluating corrective measures so that the best solution

can be identified.

v

TABLE OF CONTENTS

Acknowledgments ii

Abstract. iii

Summary iv

Implementation Statement. v

Introduction. 1

Highway 3

Driver. 16

Vehicle 18

Analysis. 20

Conclusion. 21

vi

INTRODUCTION

The mysteries of wet-weather skidding have concerned highway engineers

for a number of years. Similar vehicles influenced by similar environ­

mental and roadway factors do not always have similar reactions. It is

apparent that in such cases some subtle variation in factors influencing

these interactions made the difference. Researchers are actively collect­

ing data on the elements of wet-weather skidding. The resulting data

files are beginning to look impressive, but to be effectively utilized

the significance of these data must be fully understood. The challenge

for engineers and researchers is to understand the multiplicity of inter­

actions resulting from various combinations of the interrelated elements.

The importance of the phenomenon of hydroplaning has been only recently

identified. But hydroplaning is only a small part of the overall problem

of wet-weather skidding.

The purpose of this study has been to apply systems concepts to the

problem of wet-weather skidding. The systems approach was selected

because it lends itself to the evaluation of the interaction of variables.

The model developed in this study allows for the identification and

classification of the factors which influence skidding, but most important,

it permits examination of their interaction. Rarely is one isolated

element the sole cause of an accident, but two or more interacting ele­

ments are very likely. Particular emphasis has been paid to the highway

elements of wet-weather driving because of the amenability of these

elements to corrective action. However, researchers in other areas of

1

highway safety can benefit by identifying problem areas of concern.

This systems model is not intended to be a solution to the problem, but

is intended to clarify the problem and to place each element in proper

perspective, which should serve to identify those areas in which addi­

tional research is most needed.

2

HIGHWAY

The primary components of a wet-weather accident are: (1) Highway

Condition, (2) the Vehicle and (3) the Driver. Superimposed on these

major areas are the Meteorological and Physical Environments which affect

not just the highway condition but the vehicle and driver as well. (See

Figure 1.)

The greatest effort has been concentrated on the Highway Condition where

a large amount of data is readily available on the

variables related to wet-weather accidents. The Highway Condition vari­

ables are grouped into three areas: (1) the Highway Section, (2) the

Physical Environment and (3) the Meteorological Environment. (See Figure

2.) Some variables differ only slightly; therefore, criteria were developed

to establish their categorization. All variables dealing with geometries,

pavement and communications are included in the Highway Section. By defi­

nition, the Highway Section is that portion of the road lying horizontally

between the shoulder edges and vertically between the pavement surface and

the subsurface bottom. Some of the variables of the Communication System

coincide with those of the Physical Environment, but the effects in each

case are entirely different. The Physical Environment deals more specif­

ically with an object's size, character, placement and interaction with

geometries.

For example, the variable "guardrail;' is included under the Communi­

cation System because the guardrail conveys an informal and subtle

message to the driver as to the shape of a particular highway section.

3

DRIVER

SKIDDING ACCIDENT

VEHICLE

ENVIRONMENT

FIGURE I

4

HIGHWAY

t HIGHWAY SECTION

SKIDDING

ACCIDENT

VEHICLE

ENVIRONMENT

HIGHWAY

j ~

PHYSICAL ENVIRONMENT

FIGURE 2

5

I

I ~--J

t METEOROLOGICAL

ENVIRONMENT

Likewise, the guardrail is included under the Physical Environment be­

cause, due to the guardrail's size and placement, the driver tends to

over-respond to it. In other words, the physical existence of the guard

rail elicits an evasive response from the driver.

The Meteorological Environment, as it is discussed, was basically

identified by the U. S. Meteorological Agency. This phase of the Highway

Condition includes the variables known to constitute all types of weather

conditions and interactions.

At this point detailed consideration should be given to the Highway

Section and its three major divisions. As has already been stated, the

major areas of the Highway Section are: (1) the geometries of the highway,

(2) the pavement and its characteristics and (3) the communication system.

(See Figure 3.) In this study the scope of geometries embraces: a) hori­

zontal alignment; b) vertical alignment; and c) intersections and inter­

changes. By breaking down the geometries into these three elements, all

aspects of highway design are included. (See Figure 4.) The horizontal

alignment is divided into the tangent section and the horizontal curve

section. (See Figure 5.) Included in the tangent section are: (1) lane

width, (2) diagonal pavement joints, (3) lane transition, (4) shoulders,

(5) alignment change and (6) traffic separators. The variables of the

horizontal curve section are: (1) degree of curvature, (2) sight distance,

(3) curve transition and (4) lane width. The vertical alignment variables

include: (1) tangent grades, (2) auxiliary lane and (3) ratio of differential

grade to curve length. The intersections and interchanges category is divided

into non-channelized and channelized which differ in that the channelized

6

t HIGHWAY SECTION

PAVEMENT

I

I

L---·

HIGHWAY

PHYSICAL

ENVIRONMENT

HIGHWAY

SECTION

GEOMETRICS

FIGURE 3

7

J METEOROLOGICAL

ENVIRONMENT

COMMUNICATION SYSTEM

00

1 TANGENT SECTION

t_

HORIZONTAL ALIGNMENT

f 1

HORIZONTAL CURVE

SECTION

,..~

I I I I I I I

HIGHWAY I

SECTION ·

L~ GEOMETRICS 4

VERTICAL ALIGNMENT

•

TANGENT GRADES AUXILIARY LANE

VERTJCAL CURVES

DIFFERENCE IN GRADES RATIO OF CURVE LENGTH TO MAXI­MUM SPECIFIED BY· AASHO. .

. SIGHT DISTANCE

COMMUNICATION

SYSTEM

1'

INTERSECTIONS AND

INTERCHANGES

f t t

I I

NON-CHANNELIZED CHANNELIZED

FIGURE 4

t HORIZONTAL

ALIGNMENT

'

! I I I I I I I I L---+

TANGENT SECTION

. j

LANE WIDTH DIAGONAL

PAVEMENT JOINTS

OR MARKINGS TRANSITION OF LANES SHOULDERS

WIDTH TYPE

DISTANCE FROM LAST CHANGE OF ALIGNMENT

TRAFFIC SEPARATOR cARRIER CURB MOUNTABLE CURB CENTER LINE PAINTED OR FLUSH

GEOMETRICS

VERTICAL

ALIGNMENT

HORIZONTAL ALIGNMENT

t INTERSECTIONS

AND INTERCHANGES

' HORIZONTAL CURVE SECTION

DEGREE OF CURVATURE SIGHT DISTANCE

PASSING STOPPING

TRANSITION TO CURVE TANGENT TO SPIRAL TANGENT TO CIRCLE

LANE WIDTH

FIGURE 5

q

section considers transition and channelization type. (See Figure 6.)

. The Highway Section is characterized not only by geometries but also

by the pavement proper. Little has been done to document the effects of

the pavement variables on wet-weather accidents, but those presently in­

cluded are: (1) pavement type, (2) texture, (3) friction, (4) cracking,

(5) roughness and (6) ponding. Each of these affect the roadway surface

to some degree.

The last phase of the Highway Section for consideration is the com­

munication system. Highway communications to the driver are both formal

and informal. Formal communication devices are signs, signals and mark­

ings; informal messages are conveyed by geometries, guardrails, delin­

eators and alignment. All of these means of communication influence the

driver and their combined effect elicits a response from him. (See Figure

7.)

As previously mentioned, some of the communication elements are also parts

of the Physical Environment, but their roles differ with respect to each

classification. In the environment the existence of a physical object

affects the driver and his manipulation of his vehicle; these effects are

a function of the proximity of the object to the roadway and the vehicle

as well as the speed of the vehicle and the expectations of the driver.

Such physical objects might be vegetation, bridges and utility structures,

roadside development, other traffic, curbs, and bridge and guardrails.

Their relationship to the roadway may cause a driver to avoid them with

exaggerated maneuvers which simultaneously create potential accident

hazards. (See Figure 8.)

10

GEOMETRICS

~

t HORIZONTAL VERTICAL

ALIGNMENT ALIGNMENT

INTERSECTIONS AND

INTERCHANGES

_t t

NON-CHANNELIZED

j SIGHT DISTANCE VISUAL

IDENTIFICATION OBVIOUS DIFFICULT TO SEE

FIGURE 6

11

' INTERSECTIONS

AND INTERCHANGES

I I I I I I I I I I

f4---.J

' CHANNELIZED

I SIGHT DISTANCE TRANSITION DISTANCE VISUAL IDENt ANGLE OF

:

DIVERGENCE OF RAMP TYPE OF CHANNEL

BARRIER MOUNTABLE FLUSH

t GEOMETRICS

t FORMAL

SIGNS

INFORMATIVE DIRECTIONS WARNINGS

SIGNALS

MARKINGS EDGE LINES ARROWS STRIPING

HIGHwAY SECTION .

T PAVEMENT

COMMUNICATIONS SYSTEM

•

~

COMMUNICATIONS SYSTEM

I I I I I I I I I I I

14---.J

t INFORMAL

GEOMETRICS

GUARDRAILS DELINEATORS ALIGNMENTS

HORIZONTAL VERTICAL

FIGURE 7

12

t

HIGHWAY SECTION

HIGHWAY CONDITION

.&..

I

PHYSICAL ENVIRONMENT

I I I I I I I

PHYSICAL ENVIRONMENT

VEGETATION BRIDGE STRUCTURES UTILITY STRUCTURES ROADSIDE

DEVELOPMENT OTHER TRAFFIC

TYPE PLACEMENT VOW ME SPEED DIRECTION

CURBS GUARDRAILS BRIDGE RAILS FRONT SLOPE BACK SLOPE,

FIGURE 8

13

t

METEOROLOGICAL ENVIRONMENT

The Meteorological Environment is one over which the driver has little

control, and apparently little is known about the effect of many of its

elements on a skidding accident. This environment is composed of precipi­

tation, light, atmosphere, visibility and other less significant elements

which interact with the highway, the vehicle and the driver. Precipitation may

be the predominant element, and it varies with regard to type, intensity,

duration, accumulation and antecedent precipitation (the amount or lack of

precipitation preceding existing conditions). The atmospheric condition

is determined by the temperature, humidity, cloud cover, wind and antece-

dent temperature. The elements of light and visibility are closely inte­

grated with the main difference being that visibility concerns types and

amount of light, while light itself concerns the kind, direction and

intensity of light. (See Figure 9.)

All of these previously discussed elements and their variables make

up the total highway condition. And they directly or by way of an inter­

action affect the driver's perception and actions and the vehicle-highway

interaction.

14

~OMETRICS

HORIZONTAL I I VERTICAL ALIGNMENT ALIGNMENT

f ~~~~-il

I-' \Jl

t HORIZONTAL

CURVE SECTION

1 TANGENT

GRADE AUXILIARY VERTICAL

CURVES

_r.

INTERSEC.

INTERCHG.

~

HIGHWAY CONDITION

HIGHWAY SECTION

PHYSICAL ENVIRONMENT

1 1 r--1 __.___,, r---'--1 ------,,

f BRIDGE STR.

METEOROLOGICAL ENVIRONMENT

PRECIPITATION PAVEMENT TYPE TEXTURE FRICTION CRACKING ROUGHNESS PONDING

COMMUNICATION SYSTEM UTILITY STR. TYPE

t FORMAL

SIGNS MARKINGS SIGNALS

_1 INFORMAL

GEOMETRICS DELINEATORS ALIGNMENT GUARDRAILS

ROAD DEV. OTHER TRA.

TYPE PLACE VOLUME SPEED DIRECTION

CURBS GUARDRAIL BRIDGE RAIL FRONT SLOPE BACK SLOPE VEGETATION

INTENSITY DURATION TOTAL TIME ACCUMULATION ANTECEDENT

H LIGHT DAY NIGHT DIRE-G. OF SUN INTENSITY

ATMOSPHERE TEMPERATURE

H HUMIDITY CLOUD COVER ANTECEDENT

VISIBILITY RESTRICTIONS

POLLUTION

FfGURE 9 *-1 LIGHT

SUN MOON

DRIVER

The driver portion of the systems model is the most difficult of all

to evaluate because the driver's psychological and physiological states are

difficult to determine. The latter would require a physical examination,

and even then not all the condition variables could be determined. The

variables of physiology concern homeostasis, handicaps, the degree of drug

and alcohol intake, and fatigue. The psychological variables, such as

personality, state of mind, and emotional state are also difficult to

identify accurately because they are in a constant state of change. The

most easily determined area considered under the driver section is that of

experience. Most of the variables of one's experience are matters of

record. For instance age, training, license examination, intelligence,

level of formal education, years of driving and annual mileage are all on

file or can be established by routine examination. (See Figure 10.) All

of these variables affect the driver's perception and ultimately his overt

actions. The sum total of these interactions affects the probability of an

accident.

16

I DRIVER

l 1 I

I EXPERIENCE I I PSYCHOLOGICAL I I PHYSIOLOGICAL I +

1 t f f f i AGE TRAINING LICENSE NTELLIGENCE YEARS YEARS ANNUAL PERSONAL! TY HOMEOSTASIS

EXAM EDUCA. DRIVE. MILEAGE AGGRESSIVE DISEASE 15- SELF NONE NORMAL 0- 0- 100- NERVOUS MALAISE

20- PARENT PARTIAL ABV. NORM. 6- 5- 10,- STATE OF MIND HANDICAPED 30- SCHOOL COMPLETE BLO. NORM. 9- 10- 20,- ATTENTIVE INFLUENCE OF :

50- AGENCY 12- 35- 50,-THOUGHTFUL DRUGS SLEEPY ALCOHOL

70- 16- 100,~ EMOTIONS FATIGUE

NO RESPONSE TIRED HAPPY SLEEPY ANGRY

------ --------- :.....____ ____ -·---

FIGURE 10

VEHICLE

The last major area of concern, which affects the driver's perception

and physical actions and interacts with the highway, is the vehicle. The

vehicle is a machine with distinct characteristics which limit its per­

formance and capabilities. The dynamics of vehicular machines vary, such

as acceleration, speed, braking and deceleration capacities. The design

of vehicles differs greatly with regard to weight, engine, suspension,

brakes and power train, among other things. And last of all, a vehicle's

condition or state of repair varies significantly and influences its per­

formance. (See Figure 11.) All of these elements interact to determine

the composite vehicle condition. Then the vehicle interacts and responds

mechanically to the highway and to the driver and thereby influences the

outcome of an accident.

18

...... \C

• I .. , VEHICLE f4 • •

TYPE t

AUTO TRUCK

PICKUP 2AXLE !AXLE 4AXLE

DYNAMtcS

SPEED ACCELERATION DECELERATION BRAKING

DESIGN f

WEIGHT ENGINE STEERING SUSPENSION BRAKES TIRE TYPE POWER .. TRAIN · ELECTRICAL SAFETY ACC ES. COMFORT ACCES.

FIGURE fl

CONDITION

ENGINE STEERING SUSPENSION BRAKES TIRE CONDITION POWER TRAIN ELECTRICAL SAFETY ACCES • COMFORT ACCES.

ANALYSIS

At this point the Highway, the Drive~and the Vehicle have been

identified and proposed as having an effect on the probability of a skid­

ding accident. In its present form, the mathematical model can be used

in combination with engineering judgment and information on the variables

within the three major elements to determine the apparent causes of an

accident. These apparent causes then become the basis for the determina­

tion of corrective measures. The proposed corrective measures could

then be evaluated by engineering and economic considerations. A cost

analysis should be concerned primarily with the long term cost and cost

benefit of each corrective measure rather than with just the initial

cost. A selection from the corrective measures available is made and fed

back into the skidding accident loop. (See Figure 12.) Thus the loop

is closed and an evaluation and re-evaluation program begins in order to

find the best possible solution.

20

IRE 12

SKIDDING ACI H SYSTEMS MODEL

f CONDITION

I t IY SECTION PHYSICAL ENVIRONMENT !METEOROLOGICAL ENVIRONMENT

r t VEGETATION

GEOMETRICS

I t I !HORIZONTAL ALIGNMENT VERTICAL ALIGNMENT I I INTERSECTION AND INTERCHANGES

t t 1 1 1 TANGENT SECTION HORIZONTAL CURVE SECTION TANGENT GRADES NON-CHANNELIZED CHANNELIZED

LANE WIDTH DEGREE OF CURVATURE AUXILIARY LANE SIGHT DISTANCE SIGHT DISTANCE DIAGONAL PAVEMENT JOINTS SIGHT DISTANCE VERTICAL CURVES VISUAL IDENTIFICATION TRANSITION DISTANCE

OR MAR KINGS PASSING DIFFERENCE IN GRADES OBVIOUS VISUAL IDENTIFICATION

MENT \coM MU N ICATIO N S SYSTEM I BRIDGE STRUCTURES PRECIPITATION

UTILITY STRUCTURES TYPE fPE J t ROADSIDE DEVELOPEMENT INTENSITY

FLEXIBLE OTHER TRAFFIC DURATION

RIGID FORMAL INFORMAL TYPE TOTAL PRECIPITATION DURING i::XTURE

SIGNS GEOMETRIC$ PLACEMENT r- EVENT r---~ICTION

INFORMATIVE GUARD RAILS VOLUME LENGTH. OF TIME WATER ON

RACKING DIRECTIONS DELINEATORS SPEED

PAVEMENT ::>UGHNESS

WARNINGS ALIGNMENT fHRECTION ACCUMULATION OF WATER

ONDING SIGNALS HORIZONTAL CURBS

ANTECEDENT PRECIPITATION MARKINGS VERTICAL GUARD RAILS

TRANSITION OF LANES STOPPING RATIO OF CURVE LENGTH DIFFICULT TO SEE ANGLE OF DIVERGENCE EDGE LINES BRIDGE RAILS

SHOULDERS TRANSITION TO CURVE TO MINIMUM SPECIFIED OF RAMP ARROWS FRONT SLOPE

TYPE TANGENT TO SPIRAL BY AASHO TYPE OF CHANNELIZATION STRIPING BACK SLOPE LIGHT

WIDTH TANGENT TO CIRCLE SIGHT DISTANCE BARRIER DISTANCE FROM LAST LANE WIDTH MOUNTABLE

DAY

r- NIGHT r---CHANGE OF ALIGNMENT FLUSH DIRECTION OF SUN

TRAFFIC SEPARATOR LIGHT INTENSITY

MOUNTABLE CURB

BARRIER CURB

CENTER LINE ATMOSPHERE PAINTED OR FLUSH AIR TEMPERATURE

t HUMIDITY .- DRIVERS PERCEPTION CLOUD COVER

ANTECEDENT TEMPERATURE SPEED ...... WIND

~

:- DIRECTION

DIRECTION TRACTION VARIABILITY

VELOCITY

GUSTINESS

VISIBILITY RESTRICTIONS

DRIVERS CONTROL LOGIC TYPE OF POLLUTION

'""- DUST -SMOKE

LIGHTENING

DIRECTION OF SUN PHASE OF MOON

)RIVER f I DRIVERS STRATEGYj

t t f EXPERIENCE

I PSYCHOLOGICAL PHYSIOLOGICAL

PERSONALITY HOMEOSTASIS I DRIVERS SKILL I AGGRESSIVE DISEASE

AGE TRAINING !LICENSE EXAMI

INTELLIGENCE YEARS OF EDUCATION YEARS DRIVING 15-20 SELF NONE NORMAL 0-6 0-5 20-30 PARENT PARTIAL ABOVE NORMAL 6-9 5-10

30-50 SCHOOL COMPLETE BELOW NORMAL 9-12 10-35

50-70 AGENCY 12-16 35-

UAL MILEAGE NERVOUS MALAISE

100- 10,000 STATE OF MIND HANDICAPPED

10,000- 20,000 ATTENTIVE INFLUENCE OF:

20,000 - 50,000 THOUGHTFUL DRUGS

50,000- 100,000 SLEEPY ALCOHOL

70- 16- 100,000- EMOTIONS FATIGUE

NO RESPONSE TIRED PHYSICAL ACTIONS

HAPPY SLEEPY ~ ANGRY BRAKES

SAD STEERING

t ACCELERATION ~

SPEED

r--IMPLEMENT TYPE DYNAMIC

MAINTENANCE t---- AUTO SPEEC

REDESIGN TRUCK ACCEL

PICKUP OECEI

RECONSTRUCTION 2 AXLE BRAKI

t----3 AXLE ~ LEGISLATIVE 4 AXLE

CHANGE

~-DIRECTION TRACTION

1

J DESIGN CONDITION

WEIGHT ENGINE

ENGINE STEERING I VEHICLE-HIGHWAY INTERACTION_/--STEERING SUSPENSION

SUSPENSION BRAKES

1 BRAKES TIRE CONDITION

TIRE TYPE POWER TRAIN POWER TRAIN ELECTRICAL

ELECTRICAL SAFETY ACCESSORIES I SKIDDING ACCIDENT RATE I SAFETY ACCESSORIES COMFORT ACCESSORIES

I SELECTION PROGRAMMED COST CORRECTIVE MEASURES

t ANALYSIS t l l t I ENGINEERING I ~ r ECONOMIC r

JUDGEMENT l ENGINEERING/ DRIVER ROADWAY VEHICLE

DESIGN DRIVER GEOMETRIC$ INSPECTION

JUDGEMENT EDUCATION WIDTH DESIGN

DRIVER TEST ACCESS MAINTENANCE

COMFORT ACCESSORIES

r 1 t SKIDDING L I ACCEPTABLE COMPARATOR

ACCIDENT RATE I j CA~~ES I ANALYSIS

t 1 t ACCIDENTS t _t ENGINEERING JUDGEMENT MATH MODEL 1--- INFORMATION

ACCIDENT REPORTS

INVESTIGATION

DRIVER HIGHWAY

LAWS AND PAVEMENT VEHICLE REGULATIONS TYPE ENVIRONMENT

FRICTION

TEXTURE

CONCLUSION

The Systems Model outlined here should not be regarded as a solution

to the problem of wet-weather skidding accidents but should be viewed as

a description of the total event from which a solution may be sought.

This Skidding Accident Systems Model contains most of the known variables

which contribute to such accidents, and it is the intent that through the

use of this model new areas of needed research will be identified that

will improve the accuracy of the model. An effort has been made to keep

the model flexible so that it may be supplemented and updated with new

research findings.

21