Whenever a vehicle accident occurs, it is the police department's responsibility to determine what happened to decide who was at fault. One of the most important factors in any vehicle accident is the speed. The speed can be calculated by using the skid marks that were left on the road when the brakes were applied. The skid marks left by a motorcycle can be used to determine the speed at which it was travelling at the time of the accident.

Measure the skid mark. If there are two skid marks from the two wheels, measure them both, add them together and divide by two. This is your skid measurement.

Use the roadway surface to determine drag factor. The drag factor is different for each type of surface. For instance, a concrete roadway is 0.55 to 1.2, gravel is 0.4 to 0.8 and snow is 0.1 to 0.55.

Figure the braking efficiency. If both tires left skid marks, the braking efficiency would be 100 per cent. If only one skid mark was left, the braking efficiency would be 50 per cent.

Multiply the braking efficiency (as a percentage), the drag factor and the length of the skid mark together. Multiply that number by 30, which is a constant for this type of equation.

Figure the square-root of the number from multiplying the other factors together. This will give you the speed of the motorcycle in miles per hour. This is the speed the motorcycle was travelling.