For the 1997 data year, UMTRI's Center for National Truck Statistics collected data on rear underride as part of its Trucks Involved in Fatal Accidents (TIFA) survey. Data collected included whether the truck had a rear underride guard, whether the striking vehicle underrode the truck, and how much underride occurred. A primary goal was to evaluate rear underride of straight trucks.
Overall, 453 medium and heavy trucks were struck in the rear by a nontruck vehicle in a fatal crash in 1997. Some underride occurred in at least 272 (60.0%) of the rear-end crashes. For straight trucks, there was some underride in 77 (52.0%) of the crashes, no underride occurred in 43 (29.1%) of the fatal rear-end crashes, and underride could not be determined in the remaining 28 (18.9%) straight truck rear-end crashes. Despite the fact that three-fourths of tractor combinations had an underride guard on the trailer, underride was more common for tractor combinations. Some underride occurred in 192 (67.1%) of all 286 tractor combinations struck in the rear during a fatal crash.
In 1997, there were 527 fatalities in rear-end crashes in which the truck was struck by a nontruck vehicle. Four hundred seventy-five persons were fatally injured in the striking vehicle in rear-end collisions. Of these, at least 297 deaths occurred when the striking vehicle underrode a truck, 115 deaths occurred with no underride, and underride could not be determined for 63 deaths. One hundred fifty-seven deaths occurred in vehicles striking a straight truck; 79 involved underride. Three hundred sixteen deaths occurred in vehicles striking a tractor combination, 216 involved underride.