Traffic Fatalities and Injuries: Are Reductions the Result of ‘improvements’ in Highway Design Standards?

A cross-sectional time series database of U.S. data on fatalities and injuries is analysed using a fixed effects negative binomial regression. Data from 50 states over 14 years is used to examine the effect of various highway improvements on both fatalities and injuries. These include the total lane miles of capacity, total average number of lanes by functional road category (interstates, arterials, and collectors), lane widths and the relative balance of the various road categories within each state. Results strongly refute the hypothesis that engineering design improvements have been beneficial for reducing total fatalities and injuries. While controlling for other effects it is found that demographic changes in age cohorts, increased seatbelt use, and increases in medical technology have accounted for a large share of overall reductions in fatalities. These results have major implications for the cost benefit analysis of highway projects and for new Federal planning regulations that require safety to be considered as a planning factor.