This paper presents an analysis of the relationship between passenger car weight and occupant crash protection for single vehicle nonrollover crashes. About half of all passenger car occupant fatalities are in single vehicle crashes. In single vehicle crashes, nonrollovers account for 55 percent of the fatalities. Thus, the single vehicle nonrollover crash mode is a substantial component of the highway safety problem-about 6,000 out of 46,000 deaths a year. The paper concludes, from an analysis of national and state data, that drivers of lighter cars have a higher risk of injury than do drivers of heavier cars in this crash mode.

The authors estimate that this higher risk, coupled with the shift to lighter cars that occurred between 1980 and 1987, would result in a 5.6 percent increase in the number of moderate and greater injuries to drivers, if all other factors remained unchanged. Data suggests, however, that many factors did change. Although they cannot be quantified, it appears that occupants ofcars ofall weights are benefiting from improvements in roadway and vehicle design, increased safety belt use, reduced alcohol involvement, state and local programs to improve highway safety, and other factors.

The safety effect of these other factors, along with the weight-safety relationship in the rollover and multi-vehicle crash modes —which are not addressed in this paper— limit the applicability of the results of this analysis. While the analysis does provide an estimate of the hypothetical safety effect in the single vehicle nonrollover crash mode resulting from a shift to lighter cars, it does not allow any quantitative conclusions about the safety effect across the entire spectrum of crashes. Additional research into these crash modes is needed before such conclusions are possible.