The advent of several modern safety technologies has raised many questions as to their effect on the evidence which will present itself to an investigator at the scene of a road accident. Accident investigation techniques rely heavily on the interpretation of tyre skid and scuff marks, and the knowledge which on-scene investigators apply has been largely unchanged for 20 or more years. Improved knowledge would be of the greatest use to investigators working as part of the legal process, while road safety researchers would benefit if they were able to find evidence that a particular safety technology had come into action, and perhaps altered the outcome of an incident.
Following a review of current safety technologies it was decided to carry out a programme of experiments with a car fitted with an electronic stability control (ESC) system. The particular interest was to find what tyre marks would be laid on the ground, to discover whether they displayed any features which could be taken as an indication that an ESC system was active, and whether an established method of speed calculation based on the curvature of the tyre marks and the friction between the tyres and the road could be employed. Four different manoeuvres were chosen for the investigation: an asymmetric sine-steer, in which the car, in neutral, was steered first in one direction and then more sharply in the other, before straightening up; a similar manoeuvre in which the driver held the steering on until the vehicle had come to a halt; a step steer, in which the car was suddenly steered sharply to one side; and a step steer in a turn with “lift off”, in which the car was driven fast in a circle, and then steered harder in the same direction while releasing the throttle at the same moment.

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