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In accident reconstruction, the distance a pedestrian has been projected by an impact may be used to provide an estimate of the speed of the striking vehicle. With tyre marks becoming less common, as ABS braking is introduced, the method is gaining in importance. Speed estimation from throw distance rests on an empirical basis of field studies, which relate the distance projected to the speed of the vehicle. However field studies by themselves provide no understanding of the physical process. That understanding is important in the consideration of the effects of site characteristics, such as gradient or coefficient of friction. The paper presents the equation of motion for an idealised particle, travelling over a surface where the upward reaction from the surface varies from moment to moment, including times when the particle is airborne and the reaction is zero.

Detachment of wheels from heavy commercial vehicles has been noted in the UK. The mechanism appears to be that of a clamping failure. The compressive force of the wheelnut does not generate enough frictional holding power to prevent microscopic movements taking place between the wheel and nut. When this occurs the studs will be rapidly fatigued in bending and in addition the wheelnuts may loosen. The forces imposed by cornering reduce the compressive forces under the wheelnuts. In-plane forces, such as the ground reaction, may then be sufficient to overcome the frictional hold. The reduction of clamping force is larger when the stud is stiff. Dimensional inaccuracies make a key contribution to the problem. They arbitrarily change the designed flexibilities, they introduce fitting stresses and they create the difference in perimeters necessary for wheelnut loosening.

For many years accident investigators have been faced by the problem of estimating the projection velocity associated with a given trajectory. The most recent contributions to this topic were two papers at the 1981 AAAM but these, like earlier work, deal only with the aerial part of the trajectory, until the object first lands. In most accidents however the point of first landing cannot be determined and it is the point at which the object comes to rest which is recorded. The present paper derives an equation for the projection velocity associated with a given total trajectory. Using this equation it is possible to bracket the limits within which the projection velocity must lie, even when the angle of projection is unknown. In order to facilitate the use of this approach, data have been obtained on the frictional coefficients. This information is compared with existing field data on pedestrian trajectories.