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Vehicle Motion Human Factors

Explore the rational design of vehicles for human use and factors affecting performance, from increased speed to critical lateral displacement calculations. Understand human contact requirements and cognitive considerations in urban design. Learn about forces acting on vehicles and braking distances for safe driving.

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Vehicle Motion Human Factors

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  1. Vehicle Motion Human Factors

  2. Homework • Chapter 2: #3, 6, 7

  3. Human Factors • Rational Design of goods and services for people • Primary human requirements • increased speed • increased range • increased capacity • Secondary • safety, comfort & convenience, status

  4. Environment • Where workspace is located • effects person’s performance • lighting, noise, vibration, climate, pollutants • Man - Machine - Environment interaction • want to optimize

  5. Human Variation • Design is based on 90% of people • Top and bottom 5% not in design • who’s not included? • Adaptation & Instruction • want to limit instructions • How is a car laid out? • Where are the important components • Commonality

  6. Human Contact • Physical, Physiological, Biochemical • Size • Reach • Strength • Body Composition • Perception - Reaction • P-R, Info Processing, Motor Performance • Cognitive and Social

  7. Pedestrians • Important piece of urban design • Crosswalk placement • Social distance • Personal distance • Intimate distance

  8. Pedestrians • How does personal space change ? • Transit • airplanes • waiting areas • cars

  9. How big is a pedestrian?

  10. Visual Acuity • Contrast, brightness, illumination, relative motion • Acuity decreases with increased visual angle

  11. Perception Reaction Time • Time from stimulus to response • Depends on complexity of info • P-R 0.5 - 2.5 seconds depending on event type Wake Up

  12. Fig 2.2 pg 22 P-R times • Expectancy • Continuity – experiences of the immediate past are expected to continue • Event – Events that have not happened previously will not happen • Temporal – for cyclic events the longer a given state is observed the more likely it will change

  13. Distance covered during P-R time • 1.47Vt • Pedestrians • ~ 3.5fps, elderly pop ~3.0 fps just changed • Table 2.3 • DWI - Figure 2.3

  14. Lateral Displacement • Driver moves away from objects on the side of the road • Want to maintain a comfort zone between car and objects

  15. Lateral Displacement • Closer objects is to pavement edge the more lateral displacement • 3.3 ft for 8 ft lane • 1.8 ft for 12 ft lane • Can estimate lateral displacement • need l, v, dQ/dt

  16. Lateral Displacement • Critical rate of change in visual angle • if dQ/dt is less than critical assume collision • l = a cotQ • dl/dt = -acsc^2QdQ/dt • dQ/dt = va/(a^2+l^2)

  17. Lateral Displacement • A vehicle traveling 40 mph was observed to displace laterally when it was 300 feet from a bridge abutment placed 6 feet to the right of the path. At what longitudinal distance from the same abutment would you expect the same driver to displace laterally when traveling 60 mph?

  18. Lateral Displacement • What is critical rate of change (dQ/dt) • dQ/dt = {(40*1.47)*6}/(6^2 + 300^2) = 0.0039rad/sec • For 60mph • 0.0039 = {(60*1.47)*6}/(6^2 + L^2) • L = 368 feet

  19. Forces Acting on a Vehicle • Propulsive (M) • Resistance (R) • Centrifugal (C) • Weight (T) • ma • Supporting Forces (S)

  20. Resistance • Inherent • vehicle is moving through something • R is a function of T and V • Grade • adds resistance or increases speed • Curvature • from centrifugal force • can be eliminated w/ banked curves

  21. Grade

  22. Curvature

  23. Vehicle Motion • Superelevation e is the amount of banking in ft/ft on a curve • e + f = v2/gr depends on speed • Table 2.4 – Values for f • to negate f (no hands) e = v2/gr v in fps • e= v2 /15R v in mph

  24. Vehicle Motion • v=dx/dt • a = dv/dt • a=(dv/dx)v • vdv = adx • v =at + v0 • x = v0t +1/2(at2)

  25. Braking Distance • Db= (v2-v02)/2g(f+G) • f = 11.2fps^2/32.2 = 0.348 used for design • Not Brake type dependent – why? • NOT Weight dependent - why? • Does not account for reaction time

  26. Safe Stopping Distance • Time to perceive and respond + time to brake to a stop • P-R time =2.5s want to be conservative • SSD = 1.47V(2.5) + (v2-v02)/2g(f+G)

  27. Decision Sight Distance • Time to perceive and respond + time to brake to a stop • P-R time =2.5s want to be conservative • SSD = 1.47V(decision time) + (v2-v02)/2g(f+G)

  28. Example • How long does it take a vehicle to brake to a stop from 60 mph • On a 5% downgrade • On a 5% up grade • On ice on a 5% upgrade

  29. Dilemma Zones • Area around intersection - can’t stop can’t go –occurs when Yellow time is too short • Need proper Y • P-R time

  30. Dilemma Zones • a2 is comfortable deceleration rate • 4- 5 fps standing • 8 -10 fps seated • xo > xc no problem • xo <= xc dilemma • Cannot cross intersection in Y+AR

  31. Dilemma Zones • Can find minimum amber needed to eliminate dilemma zone • Amber should be not more than 5 seconds • Amber time = D/1.47V • Assume 1s P-R time for signal

  32. Dilemma Zones • How long should the amber interval be for the following: • Design Speed = 35mph • Intersection = 30 feet wide • Vehicle length = 15 feet • P-R time = 1 s • Stopping distance = 1.47*35*1 + (35^2-0^2)/[30(0.0348)] = 169 feet • Amber = 169/(1.47*35) = 3.28s

  33. Dilemma Zones • How long should the amber interval be for the following: • Design Speed = 35mph • Intersection = 30 feet wide • Vehicle length = 15 feet • P-R time = 1 s • Distance thru intersection= 168+30+15 = 213 ft • Amber = 213/(1.47*35) = 4.13s can use 3.28s Y + 1s AR

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