Time – Distance – Speed Relationships

1. Time – Distance – Speed Relationships

2. distance speed time _______ 40 mph 2.5 hrs

3. distance speed time 100 miles 40 mph 2.5 hrs d = S t

4. distance speed time 130 miles 65 mph ____

5. distance speed time 130 miles 65 mph 2 hr t = d / S

6. distance speed time 90 miles ______ 3 hrs

7. distance speed time 90 miles 30 mph 3 hrs S = d / t

8. Constant speed: d = S t d t = --------- S d S = -------- t

9. But in collision reconstruction it’s a little more complicated: SECONDS – FEET – MPH ?

10. 1 mile --------- = 1 hour

11. 1 mile 5280 ft --------- = ------------- 1 hour 3600 sec

12. 1 mile 5280 ft --------- = ------------- = 1.4666… 1 hour 3600 sec

13. 1 mile 5280 ft --------- = ------------- = 1.4666… 1 hour 3600 sec I use 1.47

14. mph ft/sec multiple by 1.47 30 mph (1.47) = 44.1 ft/sec

15. ft/sec mph divide by 1.47 103 ft/sec ÷ 1.47 = 70 mph

16. Constant speed: ( speed in mph )d = 1.47 S t d t = 1.47 S d S = 1.47 t

17. APPLICATIONS

18. Collision Avoidance d Sw

19. Time for pedestrian to reach POI d tw = d / 1.47 Sw Sw

20. Backing the Car tw seconds

21. Backing the Car tw seconds d Sc d = 1.47 Sc tw

22. Start of Collision

23. Start of Collision Can the impact be avoided?

24. PHASES IN IMPACT AVOIDANCE dr da REACTION VEHICLE AVOIDANCE

25. The PRT process (and impairment)

26. The PRT process (and impairment)

27. The PRT process (and impairment)

28. Recognition may not be as simple as you think!

29. Jim Sobek Clearly Visible Presentations, LLC

30. Jim Sobek Clearly Visible Presentations, LLC

31. The PRT process (and impairment)

32. The PRT process (and impairment)

33. PRT is a statistical concept ! “There is no such thing as thehuman perception-reaction time.” Dr. Marc Green visualexpert.com

35. 1.5 seconds “... is a good upper bound estimate, meaning that a substantial percentage (i.e. 85% to 95%) of reasonably alert drivers will respond within 1.5 seconds.” Paul L. Olson

36. 1.78 sec1.50 sec1.46 sec1.40 sec1.32 sec1.20 sec1.04 sec0.92 sec0.86 sec0.74 sec 90th percentile value

37. 2.5 seconds “... large enough to include the time taken by nearly all (90% of all) drivers under most highway conditions.”AASHTO Policy on Design Standards for Highways

38. How would you perform in a PRT test?

39. What is a reasonable RANGE of PRT values?

40. “The probable range of perception-response times for reasonably straightforward situations should be 0.75 to about 1.5 seconds.”Paul L. Olson, Forensic Aspects of Driver Perception and Response, 1996, p. 187

41. WAS THE COLLISION AVOIDABLE? COULD THE COLLISION BE AVOIDED BY A SOBER DRIVER OPERATING AT THE POSTED SPEED ?

42. reaction distance: the distance the vehicle moves during the operator’s PRT d = 1.47 S t

43. speed from skid marks braking distance

44. braking distance: the distance it takes for the brakes to stop the vehicle dr db

45. TOTAL STOPPING DISTANCE dr db ds = 1.47St + +

46. TOTAL STOPPING DISTANCE 30 mph, sober 106 ft 50 mph, impaired 243 ft

47. turn away (swerve) distance: the distance it takes for the vehicle to steer away from the pedestrian dTA dTA = 0.366 S √ L / f

48. TOTAL TURN AWAY DISTANCE dr db dTA = 1.47St + 0.366 S √ L / f

49. TOTAL TURN AWAY DISTANCE 30 mph, sober 79 ft 50 mph, impaired 153 ft

50. Speed estimate from video S = d / 1.47 t