Project Y.A.M. (Yaw Analysis Methodology) Vehicle Testing and Findings - Victoria Police, Accident Investigation Section

A vehicle oversteered or cornering at excessive speed results in the tyres of the vehicle loosing traction with the road surface. As a result tyre yaw marks may be left on the road surface. Yaw marks are common at fatal collision sites.

Various methods are reported to estimate the speed of the vehicle that leaves yaw marks on a road surface. The difference in each method is how to determine the radius and whether the peak or average friction is used.

Tests were conducted with four different vehicles. Variations in tyre pressures, and driver inputs of acceleration, braking and steering over-correction were investigated. Yawing followed by emergency braking with and without ABS was further studied.

The radar speed of the vehicle for each test was compared with speed estimates from the yaw marks.