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A common low speed motor vehicle collision scenario occurs in heavy traffic situations between two or more vehicles which were stopped in traffic prior to the collision. While information regarding the pre-collision spacing of the involved vehicles can be very useful to an accident reconstructionist, witness perceptions and statements regarding the distance between the stopped vehicles, prior to the collision, can be inaccurate. Physical evidence regarding precollision spacing is also unavailable in most cases. A study was conducted of several selected intersections in three major metropolitan areas in the United States of America. Publicly available aerial photography, rectified and scaled, was used to perform a statistical analysis of the distance between stopped passenger vehicles at busy traffic signalized intersections.

The equations of rotational motion used to calculate pre-impact vehicle speeds using the rotational displacement of the vehicles following a collision are well known. The technique uses the rotational momentum exchange during impact and the principle of conservation of rotational energy to calculate the post impact vehicle angular velocity from the energy dissipated during the vehicle's rotation to a stop (product of torque and rotational displacement). Integral to the calculation of the stopping torque on the vehicle is the determination of the effective rotational coefficient of friction (fr) between the tires and the roadway. The interactions of the road with the tires to produce the rotational coefficient of friction (fr) are more complex and less understood than those of linear coefficient of friction (deceleration factor). A derivation of the post impact equations of motion and the kinematics of vehicles in rotation are examined.