Fuel Efficiency and Automobile Safety: Single-Vehicle Highway Fatalities for Passenger Cars

This paper reports the results of an effort to shed some light on the relationship that might exist between enhanced standards and single-vehicle passenger car highway fatalities. Quantification of this relationship is not an easy task Not surprisingly, the literature on modeling the relationship between fuel economy and highway fatalities is very scant. Our analytic framework consists of two submodes: a corporate average fuel economy (CAFE) submodel and a single-vehicle highway fatalities submodel. Some of the variables that enter the CAFE relationship affect single vehicle fatalities, as well. The results of this study are not unequivocal in every respect. However, they indicate that enhanced standards and automobile safety need not be at odds with each other. A main message that emerges from this study is the need not to confuse car downsizing with downweighting. Quantitative studies of highway fatalities have mostly treated weight and size interchangeably, and have used only the weight variable in the fatalities equation to avoid dealing with multicollinearity. Such references as "size/weight' which lump size and weight together as if they were the same variable are not uncommon in the safety literature. Our study indicates that weight and size are not a proxy to each other, and that in single vehicle crashes they are likely to have opposite effects on safety. Men researchers choose to drop the size variable and include only the weight variable in the fatalities equation, the weight estimate may end up with a negative sign, not necessarily because weight has a beneficial effect on safety., but because the omitted size variable has a dominant beneficial effect on safety, which is picked up by the weight variable that appears in the equation.