Vehicle Collision Investigation Dr Neil Lamont Staffordshire University

Strange but true?

Estimation of speed (Skid length)

Coefficient of friction Ice (0.10-2.50) Wet Bitumen (0.45 -0.70) Dry Bitumen (0.60-0.80)

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

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 √02 + 2 x 0.6 x 9.81 x 50 = 24.26 m/s = 54.27 mph

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 √5.02 + 2 x 0.6 x 9.81 x 20 = 16.14 m/s = 36.10 mph

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 √ 02 + 2 x 0.8 x 9.81 x 20 = 17.72 m/s √ 17.722+ 2 x 0.6 x 9.81 x 20 = 23.44 m/s

Estimation of speed (Yaw marks)

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

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

Adult Head Child Head Torso Upper leg Lower leg X

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

Impact speed and the pedestrians risk of death

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

Estimation of speed (Deformation)

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)

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

Damaged vehicle

Correlation between kinetic energy and area of damage

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

Nissan Pulsar Kia Soul

Kinetic energy ½m x v2 Double the mass ½ 150 x 152 = 16875 Difference = 16875 joules Double the mass ½ 150 x 152 = 16875 ½ 300 x 152 = 33750 Difference = 50625 joules Double the velocity ½ 150 x 152 = 16875 ½ 150 x 302 = 67500

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 74897.3

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 74921.0

Kinetic energy

Estimation of speed √ √ Projectile motion Y = -3 m x = 18 m Vi = -g x2 Vi = -9.81 x 182 2 x -3 = 23.0 m/s

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

Estimation of speed Rotation Impact

Estimation of speed Roll over DR05NAL

Estimation of speed Headlight glass Furthest S = ½.v Nearest S = 0.0022,v2 – 0.00117v Fine glass is a good indication of impact location, as it doesn’t travel far.