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Lec 4, Ch 3, pp.43-58 Characteristics of the User and the Vehicle (Objectives)

Lec 4, Ch 3, pp.43-58 Characteristics of the User and the Vehicle (Objectives). Know four critical components of the traffic system Know there is considerable variability in the component characteristics – Traffic engineering is not an exact science

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Lec 4, Ch 3, pp.43-58 Characteristics of the User and the Vehicle (Objectives)

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  1. Lec 4, Ch 3, pp.43-58 Characteristics of the User and the Vehicle (Objectives) • Know four 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 • Know static and kinematic characteristics of vehicles affect the design of roads

  2. What we cover in this lecture… • Four components affecting the traffic system • Variability in the components • The human response process • Perception-reaction process • Pedestrian characteristics • Static characteristics of vehicles affecting road design • Kinematic characteristics – Acceleration capability

  3. Roads Drivers Four components affecting the traffic system Pedestrians Vehicles Control Devices General Environment

  4. Variability among the users • Variability among the drivers is the most concerned one • Average values miss 50% of the driver population  the 85th percentile often used (meaning that at least 85% of the user population must be safely covered) 85% Cumulative percentage • Examples: • Speed limit = Use the 85th percentile speed of the sampled speeds • Pedestrian walking speed = Use the 15th percentile speed of the sampled pedestrian walking speeds (Can you tell why the 15th percentile is used?) Speed

  5. The human response process Ability to see: • Static visual acuity • Dynamic visual acuity • Depth perception • Glare vision & recovery • Color vision • Peripheral vision (120-180 deg) Clear vision cone (3-5 deg) Fairly clear (10-12 deg)

  6. Perception-Reaction Process PRT = Perception + Reaction = (Detection + Identification + Decision making) + (Time needed to initiate the physical response) PIER = Perception + Identification + Emotion + Reaction (or volition) PIER = f (Complexity of the task, Level of expectancy, Variability of the drivers)

  7. PIER Distance Reaction Dist. (ft or meter) = Speed (ft/sec or m/sec)* PRT (sec) How far does the car travel during the perception-reaction process?  Affects sight distance requirement, sign placement, signal timing, etc. Example 3.1 (modified): Is this frog in crisis? 65 mph PIEV = 2.5 sec 190 ft away Speed = 65 mph = 65 x (5280 ft/3600sec) = 95.55 ft/sec Distance traveled during PIEV = 95.55*2.5 = 238.9 ft> 190 ft

  8. Pedestrian characteristics • Affects the design of pedestrian facilities and pedestrian control devices (pedestrian signal and yellow-all red interval) • Walking seed most critical – Variability exists 4ft/sec2 is used typically.

  9. Vehicle characteristics - Static • Size: Width, Length, Height, Overhang, Wheelbase  Affect lane width, vertical space under a bridge, tunnel, etc., and Turning characteristics (off-tracking) • Weight  Affect pavement design Max allowable truck size and weight See page 48 for specific values More discussion in CE561

  10. Off-Tracking Problem Fig. 3-2

  11. Acceleration Capability Acceleration characteristics: Affect  • Laying out passing zones • Freeway acceleration lanes • Intersection sight distance Acceleration capability = f (Speed of vehicle) Usually maximum acceleration rate decreases as speed goes up.

  12. Derivation of acceleration related formulas Open page 50. Use the textbook Constant acceleration case  you learned it in physics. (eq. 3.4, 3.5, and 3.6)

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