Evaluation of J-turn design performance in Missouri

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Research shows that a high percentage of crashes that take place on high-speed rural expressways occur at intersections with minor roads. One low-cost alternative design for improving safety of at-grade intersections on such expressways is the J-turn. In the last few years the Missouri Department of Transportation has converted some two-way stop controlled (TWSC) intersections into J-turns. In a TWSC intersection on a four lane divided highway vehicles accessing the major highway from the minor road could make a left turn or through movement at the intersection by crossing the major road movements. On the other hand, in a J-turn design vehicles accessing the major highway from the minor road make a right turning movement and then use a U-turn at a downstream location. The major road vehicles accessing the minor road via a left turning movement may or may not have to use the U-turn for their movements. This study evaluated the effectiveness of J-turn intersection design in Missouri using field studies, a public survey, crash analysis, and traffic conflict analysis. The field studies collected detailed video data at a J-turn site and a control site. The crash analysis included a statistically rigorous Empirical Bayes (EB) before-after safety evaluation. The EB study found that the J-turn design resulted in a 30% reduction in the crash frequency for all crashes and a 47.9% reduction in the crash frequency for all injury and fatal crashes. Both reductions were statistically significant at the 95% confidence level. The disabling injury crashes and minor injury crashes per year decreased by 86% and 45%, respectively. None of the five sites had a fatal crash occur after the J-turn was implemented. The elimination of fatal crashes and a significant reduction in disabling injury crashes are substantial safety improvements offered by the J-turn design. One of the most severe crash types, the left turn right angle crashes was completely eliminated by the J-turn. Rear-end, sideswipe, and passing crashes also decreased post