Assessment of NHTSA’s Report “Relationships Between Fatality Risk, Mass, and Footprint in Model Year 2004-2011 Passenger Cars and LTVs” (LBNL Phase 1)

The Department of Energy's (DOE) Vehicle Technologies Office funds research on development of technologies to improve the fuel economy of both light - and heavy-duty vehicles, including advanced combustion systems, improved batteries and electric drive systems, and new lightweight materials. Of these approaches to increase fuel economy and reduce fuel consumption, reducing vehicle mass through more extensive use of strong lightweight materials is perhaps the easiest and least expensive method; however, there is a concern that reducing vehicle mass may lead to more fatalities.

The relationship between vehicle mass and safety has been debated for many years. This debate has become more relevant with the advent of much more stringent federal fuel economy and greenhouse gas emission standards for new light-duty vehicles. The model year 2017 to 2025 standards are based on the footprint (wheelbase times track width) of each vehicle, with more stringent standards for smaller vehicles; the intent is to encourage manufacturers to make vehicles lighter to meet the standards while maintaining size, without compromising safety.

Lawrence Berkeley National Laboratory (LBNL) has conducted several analyses to better understand the relationship between vehicle mass, size and safety, in order to ameliorate concerns that down-weighting vehicles will inherently lead to more fatalities. These analyses include recreating the regression analyses conducted by the National Highway Traffic Safety Administration (NHTSA) that estimate the relationship between mass reduction and U.S. societal fatality risk per vehicle mile of travel (VMT), while holding vehicle size (i.e. footprint, wheelbase times track width) constant; this particular analysis is referred to as the LBNL Phase 1 analysis.