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Lec 3: Ch 3, Part IUser and Vehicle Characteristics

Objectives Know five critical components of the traffic

system

Know there is considerable variability in thecomponent characteristics Trafficengineering is not an exact science

Know what user characteristics are critical for

driving Learn how to apply braking and sight

distances

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Topics discussed in lecture

Five components

Variability in user characteristics

Critical characteristics for drivers (PRT andvisual acuity)

Other human factors affecting driving

Static characteristics CE561

Acceleration characteristics Important forintersection design

Braking performance & Stopping sightdistance

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5 Critical Components of the TrafficSystem

Vehicles Roads

General Environment

Users

Control Devices

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Variability issues

Variability among the drivers is the mostconcerned one. See Fig 3.1, 3.2, 3.3.

Average values miss 50% of the driverpopulation the 85th percentile often used

Elderly drivers? If the majority

of the drivers is old, may considerraising the percentile value iffeasible.

Baby boomers

are getting old.

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Perception Reaction Time (PRT)

PRT = Perception + Reaction

= (Detection + Identification + Decision making) +

(Time needed to initiate the physical response)

Other popular acronym = PIEV

PRT = f (Complexity of the task,

Level of expectancy,Variability of the drivers)

Refer to Fig 3-4.and pages 44-45

Reaction Dist. = Speed * PRT

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Visual acuity (Ability to read letters at

certain distances)Ability to see: Static visual acuity

Dynamic visual acuity

Depth perception

Glare recovery

Color vision

Peripheral vision (120-180 deg)Clear visioncone

(3-5 deg)

Fairly clear (10-12 deg)

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Alcohol related crashes

43825 4459941798

22716 22084

17274

51.8% 49.5%

41.3%

0

10000

20000

30000

40000

50000

1985 1990 1995

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

Total Crashes Alcohol-related %

National Transportation Stats: 1997, USDOT, BTS

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Static characteristics & Acceleration

characteristicsDesign vehicles: Basic dimensions

Usually for Semis

Acceleration characteristics: Affect

Laying out passing zones

Freeway acceleration lanes

Intersection sight distance

(This is covered in detail by CE561.)

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Braking performance

Braking distance (See p.61 of Garber for its derivation):

Db =

ui2 uf

2

2g(f G)

See Fig. 3-10 for variations in coefficient of friction &Table 3-3 for typical conservative values.

+ if G is upslope, Db gets shorter.

- if G is downslope, Db gets longer.

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Safe stopping sight distance

SSD = ui*t +

ui2 uf

2

2g(f G)

Lets review the 4uses in the textbook,

pp.53-55

Used in highway design

Used in signal timing

Used in sign placement

Used in accidentinvestigation