QUICK REFERENCE GUIDE TO VEHICLE SPEED FROM SKID MARKS

Vehicle Speed

(MPH)

Skidded Distance (Metres)

This graph is to be used only as a basic guide to give an estimate of  vehicle speeds and is not suitable for evidential purposes. No account is taken of vehicle defect, gradient or trailers.

Grieveson Partners can give an accurate assessment of speed for evidential purposes from a wide variety of evidence.

Table of Distances Travelled During Driver Reaction Times.  

Vehicle Speed

(mph)

Distance Travelled During Driver Reaction Time

considered for various reaction times (metres)

 

0.68 sec

1 sec

1.5 sec

2.0 sec

10

3.4

4.48

6.71

8.94

20

6.08

8.94

13.41

17.88

30

9.11

13.41

20.11

26.82

40

12.16

17.88

26.82

35.76

50

15.2

22.35

33.53

44.70

60

18.24

26.82

40.23

53.64

70

21.28

31.29

46.93

62.58

  When an event occurs which necessitates a car driver taking action, a certain time elapses between the necessity for action becoming apparent and the action being carried out. This time is known as the drivers REACTION TIME.

  The actual time a driver takes to react to a situation is variable and depends on numerous factors. Each case must be taken individually and all circumstances considered. The Highway Code uses a reaction time of 0.68 second which is now considered unrealistic. However, a reaction time of approximately 1,5 seconds is commonly considered a reasonable average for the majority of drivers not expecting an event to happen.

The overall stopping distance of a vehicle can be estimated by adding the reaction distance to the braking distance read from the graph overleaf.

ã Grieveson Partners