Safety Effectiveness of Super 2 Highways in Texas

Abstract

The objective of this study was to evaluate the safety effectiveness of Super 2 highways in Texas. A before–after study was performed with the empirical Bayes (EB) method, which was superior to other methods because it could address the regression-to-the-mean bias. On the basis of potential study sites identified in seven districts (Paris, Childress, Corpus Christi, Austin, Wichita Falls, Yoakum, and Bryan) in Texas, four reference groups were considered by imposition of different restrictions. Negative binomial regression models were then used to develop safety performance functions for each reference group. From the model selection process, the most restricted reference group was selected for the final analysis. For roadway inventory and crash history data, 12 years (1997 to 2001 and 2003 to 2009) of data for Texas were examined. The analysis used fatal (K), incapacitating injury (A), nonincapacitating injury (B), and minor injury (C) crashes. Property-damage-only crashes were not included. The EB analyses were carried out on five corridors with about 53 centerline miles. The results showed that the installation of Super 2 highways led to statistically significant reductions in the incidence of crashes of 35% for crashes on segments only (KABC) and 42% for crashes on segments and at intersections (KABC) on the study corridors. These findings were consistent with those of previous studies of the safety of Super 2 corridors that showed improvements in safety with installation of passing lanes, even when traffic volumes were higher than those considered under previous guidance in Texas.