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

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 effectiveness 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 sight 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.