Pedestrian throw

Pedestrian accidents are predominately an urban problem, approximately 95% of this type of accident happen on urban roads and are usually at low speed. Government figures show that vehicle speeds of less than 20 m.p.h. although causing injury are less likely to kill pedestrians however speeds greater than this will cause sufficient injury to kill, this type of collision is therefore of some considerable concern. One third of serious injury survivors and half of fatal accidents occur in such areas. Nearly 80% of the vehicles involved are motor cars or derivatives of such vehicles, 2 out of 3 pedestrians involved in accidents with such vehicles are struck by the front of the vehicle. Recorded data and tests have produced a mathematical calculation from which accidents meeting the criteria can be used to determine the speed of the vehicle involved.

By recording the facts of the accident even in those cases when a speed can not be determined the evidence is often sufficient to establish the accident circumstances. Vital clues are left in such accidents that can assist in supporting witness evidence or in the absence of such evidence in setting out probable causation. It is possible to calculate the speed of impact in such accidents using the distance the pedestrian has been thrown from the point of impact based on the premise that a momentum exchange will take place between the striking vehicle and the pedestrian at impact. As the pedestrian has little or no weight in comparison to the vehicle and little or no speed there will be direct relationship between the distance thrown and the speed of impact.

The restrictions placed on the use of this calculation are extensive and to complicate things even further there are percentage variations to be considered dependant upon the height of the individual struck and the height of the leading edge of the bonnet. The following are an example of the matters to be considered but do not cover them all:

The point of impact needs to be identified to at least a reasonable range.
The height of the bonnet of the striking vehicle must relate to the height of the pedestrian.
The pedestrian must not have been carried on the vehicle.
The pedestrian must not have bounced along the road surface.
The walking speed and weight of the pedestrian.

The most common scenario as above is that a pedestrian walking across the road is struck to the lower leg or knee by the bumper of the car involved. This effectively knocks the legs out from under the pedestrian who starts to rotate about their centre of gravity. The hip strikes the leading edge of the bonnet followed by the shoulder or upper torso which hits the bonnet and the head the lower windscreen. As the pedestrian rotates about their centre of gravity the legs raise into the air and the head and shoulders clear the vehicle as it continues on its route passing under the pedestrian who falls onto the road surface behind the car. A common description from witnesses is that the pedestrian was thrown into the air like a sack of old cloths. The car driver has usually braked to a stop and comes to rest a few metres further down the road from the point of impact and ahead of the pedestrian.

Variations on this theme can be used to calculate the vehicles speed but great care needs to be applied. Even in circumstances when a calculation is not applicable the damage to the vehicle and the injuries sustained by the pedestrian can be of very considerable use to the investigator in forming a conclusion as to what has occurred. For example the damage caused will often have a direction across the width of the car. A leg impact to the front nearside of the vehicle followed by a hip impact towards the centre line and a upper torso or head impact to the offside of the centre line of the vehicle will indicate that the pedestrian started to cross the road from the nearside. Injuries to the lower leg, hip, shoulder and head will be on one side of the body. This may indicate from which direction the car was approaching and may answer some awkward questions.

The formulae for this calculation is not given as the variables and percentage reductions used are many making this subject one that should only be referred to a competent expert making guideline calculations a very dangerous game to play.