Effectiveness Evaluation of a Modified Right-Turn Lane Design at Intersections

Abstract

From 2006 to 2014, ten right-turn approaches in the Peoria, Illinois, area were selected and reconstructed with a modified right-turn lane design. The major purpose of the modified design was to improve the line of sight for passenger vehicles attempting to turn right, while also accommodating semi-tractor trailer trucks. While the actual changes varied among intersections, the final result at each was an improvement to the approach angle for right-turning vehicles stopped to view cross traffic. Bradley University researchers were involved in a two-part study in which they (1) performed site-specific effectiveHanness evaluations of the modified sites, and (2) conducted a crash causation analysis of right-turn crashes at 116 sites in Illinois to identify geometric design variables that correlate with right-turn crashes. In the site-specific evaluation, driver behavior analyses and traffic crash–based safety analyses were performed to assess the safety performance of the modified right-turn lane design. The field investigations of driver behavior, which included a comparative “test and control” analysis at ten sites, indicated that line of site and approach angle was improved; specifically, fewer drivers had to make exaggerated head turns to complete the right-turn, there were fewer roll-and-go stops, and more vehicles stopped at the stop bar when a stop was required. Additionally, the crash-based safety evaluation, using the empirical Bayes method, revealed statistically significant reductions in crashes at the subject approaches (59.0%) and the targeted crash type, right-turn crashes at the subject approaches (59.6%) after the modifications were made. Based on these results, it is recommended that improving the right-turn approach angle by reducing the skew of the right-turn approach be considered as a safety measure for sites experiencing right-turn crashes in Illinois. The results of the crash causation analyses revealed significantly higher right-turn crashes for approaches with head-turn angles greater than 140, right-turn angles less than 45, and acute intersection angle less than 75. Recommendations on the characteristics of good candidate sites for the installation of the modified right-turn lane design in Illinois are presented in this report.