1. Vehicle Collision Investigation
Dr Neil Lamont
Staffordshire University

2. Strange but true?

3. Estimation of speed (Skid length)

4. Coefficient of friction
Ice
( )
Wet Bitumen
( )
Dry Bitumen
( )

5. Full speed rotation
Rotation slows
Peak friction
No rotation
Brake applied
Full skid

6. Single vehicle skidding to a stop
Velocity m/s
Vi = initial velocity
Vf = final velocity
S = skid length
µ = coefficient of friction
g = gravity
This calculation finds the initial velocity of a skidding vehicle (m/s) using skid length and the coefficient of friction for the road
? m/s
CoF 0.6
50 m
√ x 0.6 x 9.81 x 50 =
24.26 m/s = mph

7. Skidding plus.
The equation allows more complex collisions to be understood by combining processes together.
5.0 m/s
? m/s
20 m
CoF 0.6
√ x 0.6 x 9.81 x 20 =
16.14 m/s = mph

8. More complex linear skidding
Even where the road surface changes this can be taken into account.
0.0 m/s
? m/s
20 m
20 m
CoF 0.8
CoF 0.6
√ x 0.8 x 9.81 x 20 = m/s
√ x 0.6 x 9.81 x 20 = m/s

9. Estimation of speed (Yaw marks)

10. Finding speed from yaw marks
The maximum velocity (critical velocity) of a vehicle following a circular path (turning a bend) is determined by the limit of adhesion, ie. the point where skidding takes place.
Therefore the critical velocity (Vcrit) is related to the coefficient of friction and the radius of the bend.
Velocity m/s
Vcrit = critical velocity
µ = coefficient of friction
g = gravity
r = radius of the bend M C

11. Estimation of speed (head strike location)
> 60 mph
45 – 60 mph
30 – 45 mph
25 – 30 mph

13. Adult
Head
Child
Head
Torso
Upper leg
Lower leg X

14. Vehicle dimensions or even severe breaking, needs to be considered though
Adult
Head
Child
Head
Torso
Upper leg
Lower leg X X

15. Impact speed and the pedestrians risk of death

16. Pedestrian throw Final resting point Landing point Impact point
Trajectory
Tumbling/Slide
Initial impact
Total throw distance

17. Estimation of speed (Deformation)

18. Vehicle deformation
Simplest model shows linear increase of damage with force.
Kinetic energy
Force = Bx + A
Deformation coefficient (B) gradient
Deformation (x)
Force at which no damage (deformation) occurs (A)

19. Vehicle damage Area of damage = Wo/2 x (D1+D2)
Measurement table cm Wo D1 D2
Damage cm2 a 10 1 5 30 b 7 60 c 8 75 a b c
Using the sum of the damage, the damage can be used to estimate collision speeds d e f
RL1

20. Damaged vehicle

21. Correlation between kinetic energy and area of damage

22. Energy Equivalent Speed
EES is found by comparing photographs of damage to similar cases in an EES catalogue. Reliable estimations are obtained where the type, extent and position of damage, the type of accident (e.g. vehicle to barrier) coincide.
Ed = ½m x EES2
Ed is the deformation energy and m the vehicle’s mass
Nissan GO

23. Nissan Pulsar
Kia Soul

24. Kinetic energy ½m x v2 Double the mass ½ 150 x 152 = 16875
Difference = joules
Double the mass
½ 150 x 152 = 16875
½ 300 x 152 = 33750
Difference = joules
Double the velocity
½ 150 x 152 = 16875
½ 150 x 302 = 67500

25. Kinetic energy
The kinetic energy of an object is the energy that it possesses due to its motion.
½m x v2
70 mph
Prior to collision
Car
Weight kg (Mass)
1500 (152.9)
Velocity mph (m/s)
70 (31.3)
Kinetic energy joules

26. Kinetic energy
The kinetic energy of an object is the energy that it possesses due to its motion.
½m x v2
31 mph
Prior to collision
Truck
Weight kg (Mass)
7500 (764.5)
Velocity mph (m/s)
31 (14.0)
Kinetic energy joules

27. Kinetic energy

28. Estimation of speed √ √ Projectile motion Y = -3 m x = 18 m Vi = -g x2
Vi = x 182
2 x -3
= 23.0 m/s

29. Non linear (oblique) collisions
Estimation of speed
Non linear (oblique) collisions
Car 2 un aided resting position
Car 1 un aided resting position
Car 2
Car 1

30. Estimation of speed
Rotation
Impact

31. Estimation of speed
Roll over
DR05NAL

32. Estimation of speed Headlight glass Furthest S = ½.v Nearest
S = ,v2 – v
Fine glass is a good indication of impact location, as it doesn’t travel far.