Analysis of Rear Underride in Fatal Truck Crashes, 2008

This study was conducted by the University of Michigan Transportation Research Institute (UMTRI) to collect and analyze crash data on rear underride in fatal truck crashes in 2008. The underride data was collected as a supplement to the 2008 Trucks Involved in Fatal Accidents (TIFA) survey, which in turn supplements National Highway Traffic Safety Administration’s Fatality Analysis Reporting System file. Data was collected on the rear geometry of the rear-most unit of all trucks in the 2008 TIFA file. In addition, for all collisions in which the rear of the truck was struck, data was collected on the extent of underride, damage to the underride guard, if any, and whether the collision was offset. In addition, international rear underride protection standards were surveyed and summarized. Overall, accounting for the rear geometry of the vehicles and exemptions for certain cargo body types, it is estimated that about 39 percent of straight trucks in the crashes were required to have underride guards, and about 64 to 66 percent of trailers pulled by tractors were required to have them. Rear underride was noted in about 63 percent of rear-end-struck (RES) crash involvements. The underride was to the windshield or beyond in 26 percent of RES involvements. Vehicles with lower front geometry tended to experience more underride than vehicles with a higher front geometry. Offset impact was not associated with greater damage to the underride guard, but did tend to result in more extensive underride. There were 532 fatalities to the occupants of vehicles that struck the rears of trucks. There was some underride reported in 59 percent of the fatalities. Considering light passenger vehicles only, 403 fatalities occurred in RES involvements, with some underride in 260, or 65 percent of the cases.