Severe injury to near- and far-seated occupants in side impacts by crash severity and belt use

This study investigated the risk of severe-to-fatal injury (MAIS 4+F) to near- and far-seated front occupants in side impacts by belt use and crash severity (delta V).

1993-2007 NASS-CDS was analyzed for front-seat occupants in side impacts while they were either the near-side or far-side occupant by belt use. Light vehicles were included with model year 1994+. Injury severity was subdivided into MAIS 0-2, 3, and 4+F. The risk for MAIS 4+F injury was determined by dividing the number of MAIS 4+F by the number of exposed occupants with known injuries. Individual NASS-CDS cases were downloaded from the 1997-2007 electronic data to evaluate injury patterns causing high relative risks.

In 35+ mph side-impact delta Vs, the risk for MAIS 4+F injury was 75.4 +/- 41.0% for unbelted near-side and 48.1 +/- 14.6% for unbelted far-side occupants. The risk was 51.8 +/- 14.8% for belted near-side and 30.9 +/- 8.2% for far-side occupants. Seat belt use was 81.4% effective in preventing MAIS 4+F injury for near-side occupants and 93.5% for far-side occupants. The relative risk (RR) for unbelted compared to belted occupants was 35.9 for far-side occupants in 10-15 mph delta V crashes. The relative risk was 35.1 for near-side occupants in < 10 mph delta V side impacts. The high relative risks were associated with complex, high-speed multi-collision crashes often with occupant impacts on the windshield, steering wheel, or other frontal components and ejection.

Seat belt use was more effective in preventing severe injury (MAIS 4+F) to far-side occupants than near-side occupants in < 25 mph delta V impacts. High relative risk for unbelted occupants in low-speed side impacts was explained by the fact that the accidents were high-speed, multi-impact collisions. Severe injury was caused by ejection, impact with the side interior, or impact with the frontal components where airbags sometimes deployed.