Impact of speeds on drivers and vehicles — results from crash tests

Kim, Woon / Kelley-Baker, Tara / Arbelaez, Raul A. / O'Malley, Sean / Jensen, Jack L.
Insurance Institute for Highway Safety
January 2021

Introduction: Despite numerous studies reporting the negative impacts of increased speeds on roadways, many states have steadily raised their posted speed limits. In response to these concerns, the AAA Foundation for Traffic Safety initiated a multi-phased study to investigate the effect of posted speed limit changes on traffic safety. The first phase entailed gathering feedback from traffic engineers on how posted speed limits are set and what factors they consider in changing posted speed limits (Kim et al., 2019). The second phase, which is the subject of this report, entailed a collaborative effort with the Insurance Institute for Highway Safety (IIHS) and Humanetics Innovative Solutions to examine how vehicle crashworthiness and occupant protection degrade as impact speed increases. Towards this, three vehicle crash tests were conducted, following the IIHS test protocol.
Method: Tests were conducted at a moderate overlap frontal impact crash mode. In this mode, 40% of the maximum width of the test vehicle crashed into a deformable barrier on the driver side with the forces concentrated on the driver side of the vehicle.This test setup simulates a head-on, partial-overlap crash between two vehicles of the same weight and size travelling at the same speed. Tests were conducted at three different impact speeds — 40 mi/h for the baseline test (Test 1) and 50 mi/h and 55.9 mi/h for two higher speeds (Test 2 and Test 3, respectively).
Results: Overall, as the crash speed increased, the additional occupant compartment deformations and higher crash energy resulted in higher peak injury measures recorded by dummy sensors over the entire body region.
Conclusion: The results show that the impact speeds in Tests 2 and 3 increased the kinetic energy to the level that exceeds the capacity handled by the vehicle’s energy-absorbing structures. The remaining crash energy transferred to the occupant compartment and resulted in increased injury severity in the test dummies. This implies that the survival likelihood of the driver in the Test 2 and 3 vehicles would be considerably lower than that of the Test 1 vehicle. Speeds on the roadway are often significantly higher than those of posted speed limits and those used in crash tests. Even after accounting for braking and/or other factors that decrease impact speed, some portion of serious injury crashes in the real world occur at severities higher than those from these crash tests. Further, this study clearly shows that relatively small increases in absolute speed (5 and 10 mi/h) not only degrade the occupant survival space in vehicles with state-of-the-art crashworthiness designs but also proportionally increase the driver’s injury and fatality risk. The results and implications from the present study convey that there is a rise in occupant injury risk and compromised occupant compartment due to an increased impact speed, given other factors remaining constant. This information suggests that advocating the importance of road safety improvement in speed limit policies and prioritizing safety when setting maximum speed limits should continue.