Pedestrian injuries such as traumatic amputations, transections and decapitations are rare in traffic accidents, but are directly connected to high vehicle impact speeds.
This paper analyses a unique case of a traumatic limb amputation and a lateral decapitation from a pedestrian car collision. The driver left the scene of the accident, but at the place of impact the car’s registration plate was found. After identifying the driver and performing a vehicle inspection, it was determined that the damage on the car does not show that the impact speed was extremely high. The same conclusion was reached by the vehicle speed determination, according to accident investigation basic principles.
For more info ; http://scidoc.org/IJFP-2332-287X-04-1002.php