Federal Motor Vehicle Safety Standards Roof Crush Resistance

The purpose of Federal Motor Vehicle Safety Standard (FMVSS) 216 is to reduce deaths and serious injuries when vehicle roofs crush into occupant compartments during rollover crashes. The National Highway Traffic Safety Administration (NHTSA) has issued a supplemental notice of proposed rulemaking (SNPRM) for this standard, asking for comments on additional tests conducted by the agency since the 2005 notice of proposed rulemaking (NPRM). The Insurance Institute for Highway Safety (IIHS) does not believe the additional tests provide meaningful information for a standard requiring two-sided testing.
However, more important, we support an increase in the minimum strength-to-weight ratio (SWR) beyond the level of 2.5 initially proposed, based on new research conducted by IIHS. New study results justify increased minimum roof strength IIHS’s (2005) comment on the NPRM noted the “surprising lack of evidence” that the quasi-static test method used to measure compliance with FMVSS 216 could predict performance in real-world rollover crashes. In fact, the only research published on the subject had not found a connection between roof strength and roof damage or between roof strength and injury risk in rollover crashes (Moffatt and Padmanaban, 1995; Padmanaban et al., 2005).
In 2007 IIHS initiated a research program to evaluate what effect, if any, roof strength has on injury risk in rollover crashes. The resulting study demonstrates a very strong relationship between injury risk and performance under the test conditions used in FMVSS 216 (Brumbelow et al., 2008, attached). Increasing a vehicle’s roof strength from 1.5 to 2.5 times vehicle weight within 5 inches of plate displacement would be expected to reduce the risk of fatal or incapacitating injury by 28 percent. The findings of the new study suggest NHTSA has greatly underestimated the number of lives that could be saved by raising the minimum roof strength required by FMVSS 216. Using 11 midsize SUVs in the analysis, IIHS estimates that a minimum requirement of 2.5 times vehicle weight would have prevented 108 of 668 deaths of front-seat occupants in these vehicles in 2006. NHTSA’s NPRM estimated 13 or 44 lives per year would be saved by a new standard requiring this strength level for the entire fleet, and the SNPRM suggested new estimates could be even lower. Although many vehicles in the modern fleet have higher roof strengths than the vehicles evaluated in the IIHS study, NHTSA’s benefits estimates are overly conservative; more appropriate estimates would justify a stronger rule.

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