Dark Side: TURN RIGHT / TURN LEFT

                            

Worldwide these are easily the most common road fatalities, probably accounting for more than 50 per cent of the third of a million road deaths each year. In the densely populated areas of the globe where vehicles are greatly outnumbered by people, such as Southern Asia, parts of Africa, and the Middle East and Central America, pedestrian casualties form a significant part of the total mortality. Most pedestrians are struck by motor cars or trucks, and the type of vehicle makes a difference to the dynamics of the impact, which - unlike injuries to vehicle occupants - is an acceleration not a deceleration process. Primary injuries are caused by the first impact of the vehicle on the victim, while secondary injuries are caused by subsequent contact with the ground. Some writers also use the term 'tertiary injuries' to describe the impact with the ground, reserving 'secondary' for additional contact with the vehicle, as when the pedestrian is hurled up against the windscreen. The usual sequence of events is as follows:

 

- The height of the car bumper bar ('fender') is well below the centre of gravity of the adult pedestrian, which lies in the abdominal region. Thus the first impact tends to knock the legs from under the victim and rotate them towards the oncoming vehicle. Depending on the profile of the front of the car, the struck pedestrian is either thrown forwards in the direction of travel if the bonnet-front is high and blunt - or scooped up onto the bonnet top, as with many slope-fronted modern vehicles.

 

- If thrown forward, secondary injuries will be suffered as a result of striking the ground, as well as the primary impact on legs and often the hips. If the car speed is appreciable (anything over 20 km/hour is sufficient), the body can be thrown into the air or knocked down flat with a severe impact. The secondary injuries may fracture the skull, ribs, pelvis, arm or thigh. A further hazard is being run over by the vehicle if the victim is projected directly in front. Sometimes he may be dragged by the under belly of the car, and seriously soiled and injured, perhaps appearing at the rear if the vehicle does not stop quickly. Many impacts are on the front corner of the car and the pedestrian may then be knocked diagonally out of the path of the car. If thrown into the centre of the roadway, the person can be run down by a different vehicle overtaking in another lane or by one coming in the opposite direction on a single carriageway.

 

If scooped up, the victim will land on either the bonnet or against the windscreen or corner-supporting pillar (the 'A' frame). The flat bonnet usually does relatively little damage, though linear abrasions, brush grazes, or friction burns may be seen. Violent contact with the windscreen, especially the rim or side pillars, is the most frequent cause of severe head injury from primary impact. Scooping-up can occur at speeds as low as 23 km/hour (about 15 mph; below 19 km/hour the body will usually be projected forwards). If the speed is high, the victim can be thrown up onto the car roof, sometimes somersaulting so that the head strikes the roof. He can then slide or be flung right over the back of the car, landing behind it in the roadway. This is more likely to happen if the car does not brake, but literally drives from under the body. In most cases, the scooped pedestrian falls or is flung off on one side of the car or the other, again to suffer secondary injuries in the road and perhaps be run over by another vehicle. The usual pattern of events is that, at the instant of contact - or even slightly before – the driver will apply the brakes violently. The scooped-up victim will acquire the speed of the car by the time he lands on the bonnet, but then the vehicle decelerates. As the adhesion to the shiny surface is small, the newly acquired velocity of the body will cause it to slide off the front of the car as the latter brakes. The victim then hits the ground in front of the car, sustaining secondary injury - and may even be run over during the residua motion of the vehicle before it finally stops.

 

In a high-speed impact, which may be anything over 50 km/hour (31 mph), the body can be flung high in the air and for a considerable distance, either to the side or in the path of the car - or even backwards over the roof. In general, the severity of the injuries – both primary and secondary - will be the more severe the higher the speed. It is impossible to estimate the speed of impact from the nature of the injuries. These can be fatal even at slow speeds of the order of 10 km/hour (6 mph), yet occasionally high-speed impacts can produce only minor damage. In Ashton's (1975, 1978) series half the deaths occurred at speeds less than 48 kmlhour (30 mph). In child victims, although the general pattern of injuries is similar, their shorter height and smaller weight affects the mechanics of impact. The primary contact is higher up their body, so they tend to be hit forwards rather than rotated upwards, though many do become scooped up onto the bonnet. Children tend to be projected further by impact and may be hurled in the air at lower speeds than with adults. They are also more prone to be run over by reversing vehicles, especially trucks, as they often play between parked vehicles and - being small - are less visible to the driver. Recent safety measures on trucks include audible reversing warnings that are automatically linked to the gear-shift lever.

 

When a pedestrian is struck by a larger vehicle, such as a van, truck or bus, the initial point of impact is higher and may cause primary damage to pelvis, abdomen, shoulder-girdle, arm or head. Because of the profile of these vehicles, there is no scooping-up effect, and the victim is usually projected forwards to suffer  secondary damage from road contact and sometimes to be run over. The most common trauma is to the legs, some 85 per cent of pedestrian casualties having lower limb injuries. Abrasions and lacerations to the upper shin and knee area are typical of car bumper contact, and fractures of the tibia and fibula, often compound, are so common that they are present in a quarter of fatalities. The femur is fractured less often, but is no rarity. The midshaft may be broken or the head may be driven into the acetabulum, together with a fractured pelvis. In children, because of their small stature, the femur may be fractured by the low bumper bar. At autopsy, the skin of the lower legs should be incised to seek deep bruising, as the clothing often protects the surface from obvious marking. When a bumper (fender) strikes a leg, the tibia is often fractured in a wedge-shaped manner; the base of the Wedge indicates the direction of the impact (often from behind), the front of the wedge pointing away from the side of contact. If the leg is weight-bearing at the time of the impact, the tibia1 fracture tends to be oblique, whereas if not stressed, as when being lifted during walking, the fracture line is often transverse. When both shins are damaged, the level may be different on each side; this indicates that the person was moving at the time, with one leg raised in walking or running. Sometimes the level of injury appears too low for the normal bumper height of most cars, but this may indicate that the vehicle was braking violently at the moment of impact, going down on its suspension as the front wheels decelerated or locked, unless dip compensators were fitted. Because of impact with the windscreen, pillars and roof, together with secondary contact with the ground, the head is the next most frequently damaged region - and the one which leads to most causes of death. Any type of injury may be sustained. Traffic accidents are the most frequent cause of skull fracture, especially of the base. Fractures of chest, arm and pelvis and injuries to the abdomen follow in frequency Often the injuries are concentrated on one side, usually on the opposite side to the point of primary impact, because the body was thrown down onto the road. Because of rotation and the variable posture from being thrown off the car structure, however, the injuries are often widespread and may show no particular pattern. Soft tissue injuries are common and, apart from abrasions, bruises and lacerations, muscle laceration and crushing can occur. A characteristic lesion from running-over, as opposed to knocking-down, is the 'flaying' injury, where a rotating motor wheel tears the skin and muscle from a limb or head. The rotatory effect against a fixed limb may strip off almost all tissue down to the bone. When a wheel passes over the abdomen or pelvis, multiple parallel striae or shallow lacerations may occur near the contact area because of ripping tension in the skin. 

 

When a wheel passes over the pelvis, abdomen or head, there may be great internal damage with little surface injury. The weight of a large vehicle can virtually flatten a head, crushing the cranial vault. Often the brain is extruded through scalp lacerations, as may be the intestine through an abdominal wound. The pelvis may flatten out when run over, the symphysis or superior rami breaking, and one or both sacroiliac joints becoming detached. Any type of intra-abdominal injury may occur from ruptured liver and spleen to perforated inrestine, lacerated mesentery and fractured. umbar spine. In the chest, ribs, sternum and thoracic spine may fracture, and heart and lung damage occur from crushing or laceration from jagged ribs. A 'flail chest' is sometimes produced when a heavy wheel runs across the supine body, breaking all the ribs on each side in the anterior axillary line. Patterned injuries may be important, in that they can assist the police in identifying a vehicle in a 'hit-and-run' accident. The most common is a tyre pattern outlined in intradermal bruising and these should be measured carefully and photographed. These marks are usually caused by the skin being forced into the grooves of the tyre tread, the Edge of the raised rubber tracing out the pattern. The elevated parts do not leave bruises, but may imprint dirt on the skin. Paint fragments and glass shards are also trace evidence that must be carefully retained, as the forensic laboratory may be able to identify the make and model of vehicle involved, and match the fragments when a suspect car is examined. Parts of the vehicle may leave patterned imprints on the skin, such as headlamps, mirrors or other components. Safety regulations for manufacturers have now almost eliminated the dangerous devices such as bonnet mascots, projecting door handles and non-flexible mirrors that used to adorn older cars. Metallic and plastic objects may still be found in the tissues from time ro time. Any such artefacts must be preserved for the police in cases in which the identity of the vehicle is not known.

 

Acknowledgements:

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