In a previous experimental study, a comparison was made between a 1978 Pontiac LeMans car front with a standard bumper and the same front with a more compliant bumper developed by the National Highway Traffic Safety Administration (NHTSA). The tests were made with the two car front and bumper systems mounted at the normal bumper level 45 cm and with a lower front configuration with the bumper level 32.5 cm above the ground. The experimental biological model system developed at Chalmers University of Technology for detailed kinetic analysis of car front to leg impact sequences was used for this comparison. The tests were carried out at 30 to 32 km/h impact speed. A significant difference was found only between the standard bumper in the higher position and the compliant bumper in the lower position.

A still more compliant bumper than that used in the previous test series was produced by NHTSA and tested with the front and bumper system in the normal position 45 cm above the ground. Ten impacts to the biological model were made at 32 km/h with loaded and unloaded specimens, and five impacts were made at 20 km/h with unloaded specimens.

Damage to the knee was seen, including fractures of the knee condyles, in two tests with the loaded specimens. Knee ligament tears were observed in all the tests, indicating the importance of the inertia of the lower leg and foot when the impacts occur at knee level. The modified, more compliant bumper in this test series caused equally serious damage to the knee as did the slightly stiffer bumper in the previous series.