For occupants protected by seat belts, air bags, or both, the most frequently injured body region in frontal crashes is the lower extremities. These injuries are usually not life threatening, but they are often associated with long term impairment. The injury mechanisms are not yet fully understood. However, high local accelerations in the footwell area and the location of the feet probably play an important role in the causation of the injuries. A reduction of the footwell intrusion by structural reinforcements of the car body may therefore not be sufficient to reduce injuries. Other counter-measures are also needed.

This paper describes a new dynamic sled test method with an instrumented Hybrid III dummy in a car body, in which the toepan intrusion is simulated mechanically. The acceleration-time history of the toepan and its displacement can be varied. Toepan accelerations/intrusions as in severe frontal off-set collisions have been simulated. Two foot positions, against the toepan or at a certain distance (as if the foot was on a pedal), were evaluated.

The effect of an inflatable device, called the Inflatable Carpet (Inca), under the floor carpet in the footwell area is evaluated by this method. The Inflatable Carpet lifts the feet away a certain distance from the flooritoepan, before they are subjected to acceleration and intrusion by the toepan.

The study has shown that the acceleration of the toepan, the position of the feet relative to the toepan, and the use of the Inflatable Carpet, all significantly influenced the load on the foot and the lower leg. The use of the Inflatable Carpet reduced the foot acceleration by up to 65 % and the tibia force by up to 50 %. The tibia index was reduced by 30 to 60 %. The Inflatable Carpet therefore seems to be able to significantly reduce the risk of receiving an injury to the foot/ankle and lower leg in collisions, where violent footwell intrusion occurs.