The Role of Intrusion in Injury Causation in Frontal Crashes

In December 2003, fifteen participating Automobile Manufacturers announced the adoption of voluntary standards for geometric compatibility in frontal crashes. In an October 2003 report, Insurance Institute of Highway Safety (IIHS) estimated that an 8 to 28 percent fatality reduction might be achieved with better geometric and stiffness compatibility (O’Neill, 2003). This benefit was based on comparing the fatality risks of car occupants in car-to-car collisions and in car-to-SUV collisions. Reduced occupant compartment intrusion was cited as the principal advantage gained by compatibility improvements. However, the study did not actually examine the role that intrusion played in causing the fatalities. This study examines the magnitude of serious injuries in frontal crashes that could be addressed by reducing occupant compartment intrusion.

Each frontal vehicle-to-vehicle case in William Lehman Injury Research Center (WLIRC) data was examined to determine the cause of each injury. The injury was attributed to intrusion when injury was caused by intruding components. The study examined the intrusion related injuries with variations in: the crash severity; the injury severity and the body region injured. The database contained 182 occupants with 339 unique AIS3+ injuries and 91 with MAIS 2+ lower limb injuries. 48% of the MAIS 3+ injuries and 68% of the MAIS 2+ lower limb injuries were associated with intrusion. It was found that intrusion injury percentage for belted occupants varied from 53% for AIS3+ injuries to 100% for AIS6 injuries while for unbelted occupants it varied from 46% for AIS3+ injuries to 21% for AIS6 injuries. Lower extremities AIS2 intrusion injuries were found to be 76% for belted occupants and 60% for unbelted occupants. AIS3+ intrusion injury percentage at different crash severities varied from 29% for deltaV under 20mph to 93% for deltaV over 35mph for belted occupants and from 18% for deltaV under 20mph to 68% for deltaV over 35mph for unbelted occupants. By improving geometric compatibility, injuries in lower severity crashes may increase due to the higher levels of acceleration caused by matching stiff structures. On the other hand, injuries in higher severity crashes would significantly decrease due to reduction in intrusion. There should be an overall benefit; however, belted occupant would realize this benefit more than unbelted occupants.