In Accident Reconstruction of Low Speed Impacts, accident reconstruction and automotive engineering expert witness writes:
Low speed impacts represent substantial number of accident-related claims and deserve attention of experts in the accident reconstruction field. Low speed impacts often occur at the intersections when a moving car rear-ends a stationary vehicle which has already stopped for a light or about to resume its motion after the light turned green. In auto accident reconstruction terms, the moving car (often the one that rear-ends the stationary vehicle) is called the “bullet” and the stationary vehicle is called the “target”.
Determining the amount of energy transferred from bullet vehicle to target vehicle in a real world crash has often been attempted by applying data compiled in crash testing. This is frequently problematic for a number of reasons. First, these crash tests are conducted with a vehicle and a fixed barrier, not with the moving vehicles. Second, these crash tests also cannot be applied to low-speed impacts because the crash testing is routinely performed at speeds exceeding 30 mph, making it impossible to extrapolate the crush values to lower speed collisions.