Browse Topic: Override / underride crashes

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Influence of Impact Configuration on Rear Compartment Intrusion and Structural Countermeasures2026-26-04621/16/2026
The impact configuration has a strong influence on the rear seat survival space intrusion pattern during severe rear-impact collisions. The relative contributions of rear seat pan forward intrusion versus rear seatback intrusion vary depending on the nature of the crash. In underride impacts, the rear wheels are pushed forward into the occupant survival space from below, causing the rear seat-pan to move forward and upward relative to the vehicle interior. Conversely, override impacts tend to produce direct seatback intrusion into the rear compartment. This study used a validated computer model from the NHTSA website to simulate various types of rear compartment intrusions under different impact configurations. The analysis also assessed structural countermeasures designed to minimize occupant survival space intrusion. The results demonstrate that underride impacts primarily drive the forward motion of the rear wheels into the structure, establishing load paths that lead to structural failures and forward propulsion of the seat pan, in contrast to the seatback-dominant intrusion observed in override impacts. Furthermore, the study shows that structural reinforcements located above, and below the beltline are effective in mitigating survival space intrusion across different rear-impact scenarios.
Thorbole, Chandrashekhar, Vhanaje, Manoj G, Eknath Chopade, Santosh
Thoracic Injury Mechanisms Due to Front Seatback–Rear Seat Pan Interaction in Severe Rear-Impact Collisions: A Case Study2026-26-00051/16/2026
Severe rear-impact collisions can cause significant intrusion into the occupant compartment when the structural integrity of the rear survival space is insufficient. Intrusion patterns are influenced by impact configuration—underride, in-line, or override—with underride collisions channeling forces below the beltline through the rear wheels as a primary load path. This force concentration rapidly propels the rear seat-pan forward, contacting the rearward-rotating front seatback. The resulting bottoming-out phenomenon produces a forward impulse that amplifies loading on the front occupant’s upper torso, increasing the risk of thoracic injury even when the head is properly supported by the head restraint. This study analyzes a real-world rear-impact collision that resulted in fatal thoracic injuries to the driver, attributed to the interaction between the driver’s seatback and the forward-moving rear seat pan. A vehicle-to-vehicle crash test was conducted to replicate similar intrusion characteristics and assess the relative kinematics between the seatback and rear seat structure. Results demonstrate that seatback bottoming out under intrusion conditions significantly elevates thoracic loading. These findings highlight the need for improved rear structural design strategies to manage load paths in underride scenarios and to minimize front seatback rearward collapse and associated occupant loading.
Thorbole, Chandrashekhar
Validation of the Use of Quasistatic Force Deformation Measurements for Determining Collision Force in Low-Speed Override/Underride Collisions2025-01-50183/21/2025
The purpose of this study was to investigate the use of quasistatic force deformation (QSFD) data to represent the collision forces in low-speed collinear collisions when there is damage to vehicle body structures as well as the bumpers. In this study five full-scale underride/override crash tests were performed and simulated with QSFD data. In each crash test a bumper or a trailer underride guard on a bullet vehicle overrode the rear or front bumper of a target vehicle and damaged structures above the bumper of the target vehicle. A QSFD measurement was performed substantially similar to the vehicle interactions in the crash using a complete exemplar target vehicle that was rigidly attached to the earth. The output of a QSFD measurement is force deflection data for the vehicle pair. Each crash test was simulated using the QSFD data, the weights of the test vehicles, the closing speed of the test vehicles, and the restitution measured in the crash test. The output of a simulation was the velocity vs. time history of the target vehicle. The change in velocity (ΔV) of the target vehicle in the simulations was determined by analysis of the force deflection data. The ΔV ranged from 3.9 to 8.6 mph. The average differences between the ΔV measured in a crash test and the calculated in the simulation of that crash test was 0.16 mph. The crash pulses of the target vehicle in the simulations were similar to the crash pulses in the full-scale tests. In three of the full-scale crash tests a load cell array measured the force of the collision. The simulations using QSFD data were able to accurately predict the collision force during the crash. This work demonstrates the utility of the QSFD methodology to represent the collision forces in low-speed crashes when there is damage beyond the bumper systems of vehicles.
Gall, Jessica, Scott, William R., Bonugli, Enrique, Watson, Richard A., Fischer, Patrick
Underride in Fatal Rear-End Truck Crashes2000-01-352112/4/2000
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.
Blower, Daniel, Campbell, Kenneth L.
Impact Project: Searching for Solution to the Underride Problem98275511/16/1998
Rear underride crashes kill thousands of people yearly worldwide. Underride guards did not follow the progress achieved by the automotive safety technology. Searching for solutions to this problem, two new guards have been designed and three crash tests carried out. A new articulated, an energy absorbing conceptual guard and a guard constructed according to the European (ECE-R58) regulation were tested. Both the new guards could avoid underride, the ECE-R58 one could not. The tests pointed out that the new articulated guard could be used after a few modifications and the conceptual one needs further optimization to become commercially feasible.
Mariolani, José Ricardo L., Schmutzler, Luis O. F., Arruda, Antonio Celso F., Occhipinti, Sidney, dos Santos, Paulo Sérgio P., Stellute, Julio Cesar, Mazarin, José Celso
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