Rollover injury in vehicles with high-strength-to-weight ratio (SWR) roofs, curtain and side airbags, and other safety improvements

Abstract

Purpose: This study investigated trends in severe injury and ejection in rollover crashes involving lap-shoulder-belted drivers and right-front passengers. It was conducted because of changes in 2009 to consumer information programs and regulations related to rollover protection. The data are presented by model year (MY) of the vehicle in groups from 1995 to 2016. NASS-CDS cases with 2010-2016 MY vehicles were also evaluated to determine the crash circumstances and causes for severe injury of belted occupants in vehicles with a high strength-to-weight (SWR) roof, curtain, and side airbags and other safety improvements.

Methods: 1997-2015 NASS-CDS data were evaluated for severe injury and ejection of lap-shoulder-belted front outboard occupants in light vehicles. Crashes were grouped by front, side, rear, and rollover. The injury and ejection data were grouped by vehicle MY: 1995-1999, 2000-2004, 2005-2009, and 2010-2016. Only drivers and right-front passengers were included if they were lap-shoulder belted and 15+ years old. Severely injured occupants were defined as those with Maximum Abbreviated Injury Scale (MAIS) 4-6 or fatality (MAIS 4 + F). National estimates were made with weighted data using the ratio weight in NASS-CDS. All NASS-CDS electronic cases were evaluated for belted occupants with MAIS 4 + F injury in rollovers involving 2010-2016 MY vehicles. The crash circumstances and injuries were studied. These vehicles had high-SWR roofs to meet Insurance Institute for Highway Safety (IIHS) ratings and FMVSS 216.

Results: The 1997-2015 NASS-CDS included 2,083,776 belted front occupants in rollover crashes with 24,466 (1.17%) MAIS 4 + F injuries. The frequency of rollover crashes has decreased with modern vehicles (P < .0001). The 1995-1999 MY vehicles involved in a rollover accounted for 7.03% of all crashes (756,228/10,760,000). The corresponding proportion was 3.57% with 2010-2016 MY vehicles (81,406 vs. 2,282,062). The risk for MAIS 4 + F was 1.325 ± 0.347% in rollover crashes with 1995-1999 MY vehicles. It was 27.2% lower in 2010-2016 MY vehicles at 0.964 ± 0.331% (P < .001). There were 42,567 (2.002%) ejections of belted occupants in rollover crashes, irrespective of injury outcome. The risk for ejection was 3.042 ± 1.44% in rollover crashes with 1995-1999 MY vehicles. It was 43.6% lower in 2004-2009 MY vehicle at 1.715 ± 0.660% (P < .001) and 83.4% lower in 2010-2016 MY vehicle at 0.505 ± 0.336% (P < .001). There were 17 rollovers with MAIS 4 + F in 2010-2016 MY vehicles in NASS-CDS. Their roof strength was SWR =4.15 ± 1.05 based on 15 vehicles. Many of the collisions involved front or side impacts and then a rollover. Four cases involved 16- to 30-year-old drivers in extremely high-speed loss-of-control crashes resulting in >10-cm vertical roof deformation or substantial roof deformation based on photos. The roof strength (SWR) of 4.20 ± 1.0 was not sufficient to prevent roof deformation in these crashes.

Conclusions: This study found a reduction in severe injury and ejection risk with modern vehicles. It indicates that vehicle safety has improved in response to IIHS and NHTSA efforts to expand the array of safety requirements and increase performance so that newer models are safer than earlier ones. There has been an incremental improvement in safety due to these advances.

Keywords: Rollovers; SWR; belted occupants; ejection; roof strength; severe injury.