roaduser and vehicle characteristics

8/13/2019 Roaduser and vehicle Characteristics

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UNIT II

ROAD USER AND VEHICLECHARACTERISTICS


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Agenda

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Road User Characteristics: Diversity

Road User

Human & Vehicle Characteristics

Factors Affecting Road Traffic

Methods of measurements

Concept of PCU for mixed traffic flow


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Review of Traffic System Components4

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ControlDevices

Vehicles

Roadways Road users

GeneralEnvironment

Pedestrian Passenger

DriverBicyclist


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Dealing With Diversity (behavior)

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Drivers & other road users-widely varying characteristics.

Traffic controls could be easily designed if all driversreacted to them in exactly the same way.

Safety could be more easily achieved if all vehicles haduniform dimensions, weights, & operating characteristics.

Why complex ??No two road users are the same

The traffic engineer must deal with elderly drivers as wellas 18-year-olds, aggressive drivers and timid drivers, anddrivers subject to myriad distractions both inside andoutside their vehicles.


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Most concerned one.

Most design practices follows normaldistribution & not averagecharacteristics.

A normal distribution defines the proportions of thepopulation expected to fall into these ranges. Because of

variation, it is not practical to design a system for averagecharacteristics. If a signal is timed, for eg., to accommodatethe average speed of crossing pedestrians, about half of allpedestrians would walk at a slower rate and be exposed to

unacceptable risks.


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Most standards are geared to the 85thpercentile or 15thpercentile characteristics.

Speed limit -85thpercentile speed

Pedestrian walking speed -15thpercentile speedWhy walking speed is 15thpercentile??

A percentile is a measure used in statistics indicating the value at orbelow which a given percentage of observations in a group of

observations fall.

In terms of walking speed, safety demands to accommodate slowerwalkers, as only 15 % of the population walks lesser than this value.Considering driver reaction time, 85th percentile is used, as 85% of

population has a reaction time which is equal to or lesser than this.


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Diversity (Vehicles)

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Highways must be designed to accommodatemotorcycles, the full range of automobiles, and awide range of commercial vehicles (double and

triple-back tractor-trailer combinations). Thus, lane widths, for example, must accommodate

the largest vehicles expected to use the facility.


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Addressing Diversity through

Uniformity

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Agenda

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Road User Characteristics: Diversity

Road User

Human & Vehicle Characteristics

Factors Affecting Road Traffic

Methods of measurements

Concept of PCU for mixed traffic flow


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Human Factors affecting Road User

Behavior (Driver Characteristics)

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Physiological Factors

Permanent

Temporary

Mental Characteristics

Psychological Factors

Environmental Factors


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1. Physiological Factors

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Measurable & usually quantifiable

Permanent

Vision

Hearing Physical Strength

Perception- Reaction Process (reaction to trafficstimulus)

Temporary Factors which affect road users efficiency (effect of

alcohol, drugs, fatigue and illness)


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(I) Vision

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The most important characteristic of drivers is their

ability to see!!

Evaluate the object size, shape, color

Estimate distances and speed of bodies Complexity of Vision

Light rays from objects refracted through lens-

brought to focus on retina image formed on

retina- transmitted to brain through optic nerves

Research has shown that approximately 90% of the

information that a driver receives is visual


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(a) Vision FactorsVisual Acuity

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Visual Acuity- ability to see fine details of an object

Static visual acuity

ability to identify an object when both object and driver

are stationary.

Eg: Chart Reading Exercise

Dynamic visual acuity

ability to clearly detect relatively moving objects

not necessarily in the drivers direct line of vision

Eg: Traffic sign reading while moving


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Visual Acuity- Normal Vision

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Visual Acuity : 20/D in foot syste


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Normal vision is taken to mean that in a well lit environment aperson can recognize a letter of about 1/3 inch in height at adistance of 20 ft then the visual acuity of the person is 20/20.

Normal visual acuity : referred to as 20/20 vision, the metricequivalent of which is 6/6 vision.

A vision of 20/40 is half as good as nominal performance.

A vision of 20/10 is twice as good as nominal performance.

If a person has 20/40 visual acuity means, he can see the objectat a distance of 20 ft (wrong vision) when a distance of 40 ft issufficient for normal vision. From a distance of 20 ft he canhave normal vision by providing the object twice as large as theprevious one.


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Solve!!!

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A driver with 20/20 vision can read a sign from a distanceof 90 ft.

(a) If the letter size is 2 inch, how close would a person with20/50 vision have to be in order to read same sign??

(b) For the given definition of normal vision, calculate height oflettering that a driver with 20/60 vision can read from a distanceof 90 ft and 36 ft.


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(b) Vision FactorsField of Vision

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Acute vision or clear vision cone3to 10around the line of sight;

legend can be read only within this narrow field of vision.

Fairly clear vision cone10to 12around the line of sight; Satisfactory Vision

color and shape can be identified (locating traffic signs &

signal)

Peripheral vision-

160in horizontal direction and 115in vertical direction

movement of objects can be detected

For detailed attention

driver has to turns his head, tomake ob ect in clear vision cone


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Field of Vision

Ref: Roger P Roess, Traffic Engineering Textbook


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LECTURE 3

UNIT 2, Road User Characteristics

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Average Citation Index

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Effect of speed on visual Acuity-

Lateral Displacement

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Driver moves away from objects on the side of the road

Want to maintain a comfort zone between car and objects

Closer objects is to pavement edge, the more lateral displacement

Can calculate Critical rate ofchange in visual angle


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Solve!!!!

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A vehicle traveling 18m/s was observed to

displace laterally when it was 91.5m away

from a bridge abutment placed at a distance of

1.83 to the right of his path. At whatlongitudinal distance from the same abutment

would you expect the same driver to displace

laterally when traveling at a speed of 26.82

m/s?


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(c) Vision FactorsGlare Vision and

Recovery

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Glare Vision - decrease ability for a driver to see and causesdiscomfort for the driver.

Glare Recovery - time it takes for a driver to recover from theeffects of glare after passing a light source.

Research has shown that the time to recover from dark to lightconditions is 3 secondsand 6 seconds to recover from light to darkconditions.

Glare Vision is a problem for older people who drive at night.

Glare effects can be minimized by reducing the brightness oflights and positioning lights further from the roadway andincreasing the height of the lights.


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(e) Vision Factors Depth Perception

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Depth Perception affects the ability of a driver to

estimate speed and distance.

Extremely important on two-lane highways when a

vehicle is passing another vehicle with traffic

approaching the passing vehicle.

The ability of a driver to estimate speed, distance, size

and acceleration is generally not very accurate.

Traffic control devices are standard in size, shape &colour provides a wide range of drivers sufficient

information to make important decisions.


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(II) Hearing Perception

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Hearing is an aid to the road-user which can at times bevery vital.

The sound of a horn or the sound of the nearing vehicle

itself can alert a pedestrian to safety. Typically hearing is only important when emergency

vehicles are sounding a warning to get out of their way.

Loss of hearing ability is not a serious problem, since it can

normally be corrected by a hearing aid.

(III) P ti R ti


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(III) Perception- Reaction

Process

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The process through which a driver evaluates & reacts to a stimulus.The time it takes to go through this process is called a PIEV time.


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PIEV or PRT

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Detection:In this phase, an object or condition of concern enters thedrivers field of vision, and the driver becomes consciously

aware that something requiring a response is present.

Identification. In this phase, the driver acquires sufficient

information concerning the object or condition to allow theconsideration of an appropriate response.

Decision. Once identification of the object or condition is

sufficiently completed, the driver must analyze the

information and make a decision about how to respond. Response. After a decision has been reached, the response is now

physically implemented by the driver.


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Factors Affecting PRT

Physiological Factors

Psychological Factors

Complexity of Reactions (Type of problem, may vary from .5s to 4s)

Environmental Condition

Temporary Factors (Presence of Drugs or Alcohol, fatigue)

AASHTO Recommendations (American Association of State

Highway and Transportation Officials) For braking reactions on Highways:

PRT: 2.5 seconds (90th percentile)

For reaction time to traffic signal PRT: 1.0 Second (85th percentile)


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Reaction Distance

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critical impact of PRT - is the distance the vehicle travelswhile the driver goes through the process.

driver aware of event.apply foot on brake

During PRT- vehicle travels in its initial speed

d = reaction distance(m),

t = reaction time (s),

S = initial speed of vehicle, km/h

Reaction Dist.= Initial Speed PRT (sec)d = 0.278 S.t


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Reaction Distance

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Example : Is this frog in crisis?

S=65 m/s, t=2.5s

Soln:

Speed =65

Distance traveled during PIEV = 65*2.5

= 162.5 m> 80 m

Deceleration begins only when the brake is engaged- onlyafter perception-reaction process has completed

80 m away


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1 (b) Temporary Physiological FactorsImpact of drugs and alcohol on road users

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P l f l h l l d RTI i


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Prevalence of alcohol related RTIs inSouth AsiaHospital based studies.

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Ref: Road Traffic Injuries, (2004). R. G. Gururaj, National Institute of Mental Health

and Neuro Sciences; Bangalore


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Who are the victims???

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Every time you drink alcohol or take drugs and then driveyou risk causing death or serious injury to yourself andother road users.

Blood Alcohol Concentration [BAC]

Effect on alcohol/drugs

What does the law say???

Indian practice of law- need to be changed????


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B.A.C [Blood Alcohol Concentration]

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amount of alcohol in the blood stream [Ref: Kadiyali Text Book]


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FACTORS AFFECTING BAC

Amount consumed Persons body weight

Kind of alcohol

Time Spent Drinking

Gender

Food (empty stomach ornot)
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Alcohol and Mental Abilities

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Acts like an anesthetic on the brain, slowing down activity


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Psychological Effects

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o Attention

o Memory

o Emotions

o Aggression

o

Tolerance

o Driver effected by alcohol has decreased ability to

reason and make sound judgments


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Impaired Vision

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Side Vision

Visual Acuity

Color vision

Eye Focus

Double Vision Distance Judgment


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Alcohol and Space Management

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After drinking,the driver maytend to stare at

the center line.


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Reaction Time and Coordination

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Risk-Taking Problem


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Drugs and Driving

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Perception

Judgment

Coordination

Vision

Mood


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What does the law says??

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Breathalyzer: Breath testingwhich measures micrograms ofalcohol (mcg) per litre of breath

Evidential breath test-readingis over 400 micrograms per litreof breath - charged with EBA(excess breath alcohol)

Blood test- measure thenumber of milligrams of alcohol(mg) per 100 millitres (ml) ofblood or whether drugs are inyour system.

Comparison of law in other


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Comparison of law in other

countries

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BAC limit in different countries

USA: 100 mg/100 ml (legal offence)

Sweden: 50 mg/ml

U.K: 100 mg/ml

Norway: 50 mg/ml

India: is there any limit?????

India: Motor Vehicle Act (1972): BAC more than 0.08%- fine of Rs. 2000

- 6 months imprisonment

- both


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2. Mental Characteristics

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Knowledge, skill, intelligence experience & literacy

Knowledge of vehicle characteristics, traffic behavior, driving

practice, road rules and psychology of road users - safe traffic

operations.

Reactions to certain traffic situations become more spontaneous

with experience.

Understanding the traffic regulation and special instruction andtimely action depends on intelligence and literacy.


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3.Psychological Factors

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difficult to measure and to quantify

a) Personality of a person

b) Emotional Factors

AttentivenessFear

Anger

Impatience

Attitude towards traffic rules & regulationsmaturity

How to consider psychological factors in design???

-only through enforcement (licensing procedure)

Psychological factors affecting on road


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Psychological factors affecting on road

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Having the physical ability to operate amotor vehicle is really only half the picture

Being in the right psychological and

emotional state - having the right attitudes,traits, and motivation is also essential to drivingsafely, being courteous, and avoiding accidentsand traffic citations.

Driver Behavior Controlling


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Driver Behavior Controlling

Emotions

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Driving experience

alcohol / drug consumption

inexperience in identifying and handling hazardous situations

over-confidence in abilities

personality structure

poor judgment

excessive speed

attitudinal factors such as risk-taking propensity.


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Improvement measures

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Road Rage- who lose control ofthemselves & react violently,improperly and dangerously!!!!!

Improvement measures

Vigorous enforcement

Education programs

Medical Helps


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Pedestrian &VehicleCharacteristics

Lecture 455

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Surprise Test No.1

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A driver with a perception-reaction time of 2.5

seconds is driving at a constant speed of 75

mph when he observes that an accident has

blocked the road ahead. Compute the distancethe vehicle would travel before the driver could

activate the brakes.


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Pedestrian Characteristics

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4.0 feet per second (ft/s) = 1.2 meters per second (m/s)


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Gap Acceptance

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roaduser and vehicle characteristics

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