United States Department of Transportation
i
Identifying priorities for improving rear seat occupant protection.
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2009-03-01
[PDF-1.02 MB]
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Abstract:This project helped to identify priorities for improving the safety of rear seat occupants through a literature review and NASS-CDS injury analysis. The literature review covers injury patterns of rear seat occupants, new safety technologies intended for the rear seat, studies of rear seat belt and seat geometry, and methods for assessing belt fit; key points follow. Most rear-seat cushion lengths exceed the recommended length of 440 mm intended for accommodating adults. Since children make up 70% of rear seat occupants, built-in booster seats with shorter cushion lengths designed to accommodate children aged 5-8 would be beneficial. Front seats tend to have steeper outboard lap-belt angles, more forward shoulder belt anchors, and narrower spacing between lap belt anchorages than in the rear seat; target lap belt angles in the rear seat should range from 45 to 70 degrees. Booster seats are potentially more effective at mitigating poor lap belt geometry than poor shoulder belt geometry, so improving shoulder belt geometry in the rear seat should have higher priority. Load limiters, seatbelt pretensioners, and inflatable belt systems are potential countermeasures for reducing thoracic injury for rear seat occupants. If load limiters are installed in rear seats, the amount of available space for occupant displacement would be more important to consider in the rear seat than in the front seat.
The NASS-CDS database was first used to identify rear-row occupant seating patterns. In the second row, adults tend to sit on the right side, but this is not true for children. Vans are the only vehicle type with substantial numbers of 3rd row seating. The ages of rear seat occupant vary substantially with driver age. Drivers aged 16-25 most likely have other 16-25YO or 0-4YO occupants in the rear seat. For drivers aged 26-50, 85% of their rear seat occupants are under aged 16. Drivers over age 50 have the greatest proportion of passengers over age 50 in the rear seat.
From the injury analysis, seating in the rear seat is protective in terms of fatality and injury reduction, regardless of restraint use, except for rear impacts. The back of the front seat is a common injury contact point for rear-seat occupants. Studies of belt restraints have seldom found a difference in effectiveness between the front and rear seat. Most common injury contact points in side impact for belted children are on the lower rear quarter of the rear window. The presence of other occupants in the rear seat provides some benefit in injury reduction for children involved in side impacts, possibly by limiting lateral movement. Pediatric abdominal injury patterns indicate that the rear seats of minivans provide an environment with lower risk of abdomen injury compared to the back seats of passenger cars and SUVs. Pediatric injury rates are similar for children riding in SUVs and passenger cars, as potential benefits of a heavier vehicle are offset by a greater tendency to be in rollovers. Presence of a three-point belt rather than a lap-only belt reduces pediatric risk of AIS2+ injury by 81%. The presence of a shoulder belt in the center rear seating position usually only affects seating practices when there is a single child occupant in the rear seat.
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