Data on towaway accidents involving 1973- and 1974-model American passenger cars were collected according to a systematic sampling plan in order to measure 1974 restraint system performance. The data on 5,138 drivers and right front passengers were collected by three organizations:​ Calspan Corporation, Highway Safety Research Institute, and Southwest Research Institute. Analysis of the data showed that the 1974 ignition interlock system increased full restraint system usage by a factor of 10 over 1973 cars. The 1974 full restraint system (lap and upper-torso belts) also demonstrated a greater reduction in severe injuries (AIS≥2) than the 1973 lap-belt-only system. Paradoxically, little reduction in 1974-model severe injuries was found when the two model years were compared, although no attempt was made to control for confounding factors in the accident cases.

Injury patterns were explored in terms of the rate of occurrence of specific injuries by body region, lesion, and injury source. All restrained occupants sustained a lower rate of specific injuries than unbelted occupants, and fully restrained occupants had a greater probability of receiving fewer injuries than lap-belted occupants. Restrained occupants received fewer head, face, extremity, and chest injuries and more neck, abdomen and pelvis injuries. The rate of face injuries with full restraints was half the rate of lap-belt-only occupants. Full restraints also reduced the incidence of steering-assembly and front-interior injuries but did not eliminate them.