Ejection and Severe Injury Risks by Crash Type and Belt Use With a Focus on Rear Impacts

Purpose: This study investigated the risk of severe-to-fatal injury (MAIS 4+F) with complete and partial ejection by crash type and belt use with a focus on ejection in rear impacts. Methods: 1993–2007 NASS-CDS was analyzed for crashes with complete and partial ejection. The effect of belt use was investigated and crashes were grouped by front, side, rear, and rollovers. Light vehicles were included with model year 1994+. Injuries of severity MAIS 4+F and AIS 3–6 by body region were determined by crash type, belt use, and ejection status. NASS-CDS electronic cases of complete ejection and serious injury were evaluated to determine the circumstances in rear impacts. Results: For unbelted occupants, the highest risk for complete ejection is in rollovers (16.4 ± 1.1%) and the risk for severe injury is 37.6 ± 2.7%. The lowest risk for complete ejection is in frontal crashes (0.97 ± 0.22%), but the risk for serious injury is 31.3 ± 6.2% when ejection occurs. The risk for ejection is 2.7 ± 1.5% in rear impacts with a 7.4 ± 3.4% risk for severe injury. For belted occupants, the highest risk for complete ejection is in rollovers (0.068 ± 0.022%) and the risk for severe injury is 25.9 ± 13.3% when ejection occurs. The relative risk for ejection is 193 times greater for unbelted compared to belted occupants in all crashes with a range of 100 times in frontal crashes up to 847 times in rear impacts. Unbelted occupants have 20 times greater risk for severe injury when completely ejected and 18 times greater risk with partial ejection compared to nonejected occupants. Belted occupants have a 77 times greater risk of severe injury when completely ejected and 37 times greater risk when partially ejected. Conclusions: Ejection involves significantly higher risks for severe injury in all crash types. The relative risk for MAIS 4+F injury is 20 times greater for unbelted and 77 times greater for belted occupants who are completely ejected compared to nonejected occupants. Ejection of occupants in rear crashes often occurs during vehicle yaw motion after the primary impact.