This study was conducted to assess the occupant restraint use and injury risks by seating position. The results were used to discuss the merit of selected warning systems. The 1989-2015 NASS-CDS and 2017-2021 CISS data were analyzed for light vehicles in all, frontal and rear tow-away crashes. The differences in serious injury risk (MAIS 3+F) were determined for front and rear seating positions, including the right, middle and left second-row seats. Occupancy and restraint use were determined by model year groups.
Occupancy relative to the driver was 27% in the right-front (RF) and 17% in the second row in all crashes. About 39% of second-row passengers were in the left seat, 15% in the center seat and 47% in the right seat.
Restraint use was lower in the second row compared to front seats. It was 43% in the right-front and 32% in the second-row seats in all crashes involving serious injury. Restraint use increased with model year groups. It was 63% in the ‘61-‘89 MY vehicles and 90% in the ‘10-‘22 MYs for drivers. The corresponding rate was 59% and 91% for right-front passengers, and 48% and 91% for second-row passengers.
Overall, the injury risk was 2.59% ± 0.20% for drivers, 2.52% ± 0.16% for RF passengers and 1.70% ± 0.16% for second-row passengers in all crashes. The risk was significantly higher (p<0.001) for RF passengers than for second-row occupants in all crashes. Injury risks were significantly higher in RF passengers in frontal crashes (2.58% ± 0.20% v. 1.43% ± 0.24%, p<0.001) than second-row occupants, but lower in rear crashes (0.63% ± 0.15% v. 0.99% ± 0.20%, p>0.1). The injury risk was lowest in modern (‘10-‘22 MY) vehicles compared to other model years.
For second-row occupants, the risk was highest in the right-rear seat in all crashes and in frontal crashes, at 1.91% ± 0.23% (1.45%-2.36% 95th CI) and 1.82% ± 0.49% (0.86-2.78 95th CI) respectively. The risk was 41% higher (p< 0.06, 0.75% diff with 0.21%-1.70% 95th CI) for right-rear than left-rear occupants in frontal crashes. The injury risks were similar in rear crashes.
The rear seat is still the safest seating position overall, even with lower restraint use in rear seats. Current mandated warning systems to place children in the rear seat are relevant. Regulations, policies, seatbelt laws and test programs seem successful in increasing restraint use and reducing injury rates to front-and rear-seat occupants. Some have suggested adding a warning to place children behind empty front seats if possible. This would tend to move children to the right side of the vehicle as the left front seat is always occupied. However, the results from this study showed that the overall injury risk was higher in the right-rear seat than in the left. The results were however only statistically significant in frontal impacts.