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In support of the European Enhanced Vehicle-safety Committee (EEVC) research program and through it, the International Harmonization of Research Activities work on compatibility, TRL is investigating the compatibility of cars in frontal and side impact scenarios. Initial research has focused on identifying the major factors which influence compatibility and determining the extent to which they might influence injury outcome. Experimental crash test research is backed with Finite Element simulation modeling. For frontal impacts, full-scale testing has been used to examine the influence of vehicle mass, stiffness, structural interaction and geometry. The modeling work has studied how non-contact, deceleration-related injuries might be minimized by optimizing the deceleration pulse.

Those responsible for designing cars to meet the European Side Impact Test Procedure are tending to find it more difficult than they originally expected. The conventional wisdom has been that strengthening the car and providing padding should improve protection. However, many are finding that attempts to meet the test requirements, by reducing door intrusion or intrusion velocity, are proving ineffective. Extensive research carried out at TRL has helped to explain why strengthening the car side is ineffective. It has also given an insight into the side impact injury process and provided design guidelines which can be used to ensure that cars meet the test requirements. The difficulties experienced by car designers may explain why alternative test procedures have been suggested and proposals have been made which would reduce the severity and effectiveness of the full scale test procedure.

Accident research has shown that intrusion into the passenger compartment is the major cause of fatal and serious injuries suffered by restrained car occupants in frontal impacts. Current frontal test procedures, which use rigid barriers impacting the full car width, generate high vehicle decelerations and seat belt loads but very low levels of intrusion. In accidents, few serious or fatal injuries result from seat belt loading whereas over two thirds of such injuries, suffered by seat belt wearers, have been shown to be due to contact with intruding structures. The need for some form of asymmetric test has been recognised for some time but more recently it has become clear that the use of rigid barriers is misleading car design. An offset impact test using a deformable barrier face overcomes the problems seen with the rigid barrier whilst also providing asymmetric loading.