Impact of Belt Use by Rear-Seat Occupants on Injury Severity of Belted Drivers in New Jersey

In January 2010, legislation in New Jersey required all occupants of vehicles to wear seatbelts regardless of seating positions. Although it is known that an unbelted rear-seat passenger affects the safety of the driver, the level of the impact is not clear. The objective of this research was to identify the factors that influenced the injury severity of a belted driver with and without rear-seat occupants. Injury severity models were developed with crash data from the Fatality Analysis Reporting System for New Jersey for 2004 to 2006. The results indicated that the probability that a driver or right-front-seat occupant would sustain more-severe injuries was higher when a left-backseat, middle-backseat, or right-backseat occupant was unbelted. For vehicles with two back-seat occupants (left-back and right-back), coefficient values for these variables indicated that lack of seat belt use by either occupant affected the injury severity level of a belted driver. The results showed that the right-backseat occupant had the greatest effect on the injury level of drivers compared with the left-back and middle-back occupants. Although seat belt use by a backseat occupant was found to affect the injury severity of a belted driver, this research demonstrated that the effect became more significant or increased as the number of backseat occupants in the vehicle increased.