Lec 3: Ch 3, Part I User and Vehicle Characteristics Objectives Know five critical components of the traffic system Know there is considerable variability in the component characteristics – Traffic engineering is not an exact science Know what user characteristics are critical for driving Learn how to apply braking and sight distances

Topics discussed in lecture Five components Variability in user characteristics Critical characteristics for drivers (PRT and visual acuity) Other human factors affecting driving Static characteristics  CE561 Acceleration characteristics  Important for intersection design Braking performance & Stopping sight distance

5 Critical Components of the Traffic System Vehicles Roads General Environment Users Control Devices

Variability issues Variability among the drivers is the most concerned one. See Fig 3.1, 3.2, 3.3. Average values miss 50% of the driver population  the 85 th percentile often used Elderly drivers?  If the majority of the drivers is old, may consider raising the percentile value if feasible. Baby boomers are getting old.

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 Reaction Dist. = Speed * PRT

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 ( deg) Clear vision cone (3-5 deg) Fairly clear (10-12 deg)

Alcohol related crashes National Transportation Stat’s: 1997, USDOT, BTS

Static characteristics & Acceleration characteristics Design vehicles: Basic dimensions  Usually for Semi’s Acceleration characteristics: Affect   Laying out passing zones  Freeway acceleration lanes  Intersection sight distance (This is covered in detail by CE561.)

Braking performance Braking distance (See p.61 of Garber for its derivation): D b = u i 2 – u f 2 2g(f ± G) See Fig for variations in coefficient of friction & Table 3-3 for typical conservative values. + if G is upslope, D b gets shorter. - if G is downslope, D b gets longer.

Safe stopping sight distance SSD = u i *t + u i 2 – u f 2 2g(f ± G) Let’s review the 4 uses in the textbook, pp  Used in highway design  Used in signal timing  Used in sign placement  Used in accident investigation