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

January 2021

Introduction: Despite numerous studies reporting on 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 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. The second phase, which this report details, involved 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 speeds increase. Towards this, three vehicle crash tests were conducted. Method: Tests were conducted at a moderate overlap frontal impact crash mode, following the IIHS test protocol. Tests were conducted at three different impact speeds — 40 mph for the baseline test (Test 1) and 50 mph and 55.9 mph for the two higher speeds (Test 2 and Test 3, respectively). Three 2010 Honda CR-V EX vehicles were selected, as they represented the average age of vehicles (11.8 years in 2019) on today’s U.S. roadways and earned the top rank in crash test ratings. All three had comparable specifications including manufacture date, vehicle mileage, and drive type. 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. Only the baseline test vehicle would earn an IIHS rating of good in the overall evaluation, which is derived from the ratings for the injury measures, structure, and restraints and kinematics components. Tests 2 and 3 would earn a poor overall score, with Test 2 results heavily influenced by the elevated head injury measure, and Test 3 by elevated injury measures to vital body regions and the heavily compromised occupant compartment. 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.