Study Details

Study Title: Evaluation of J-turn Intersection Design Performance in Missouri

Authors: Edara et al.

Publication Date:DEC, 2013

Abstract: 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 the 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. This study evaluated the effectiveness of the J-turn intersection design in Missouri utilizing 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 before-after safety evaluation of five J-turn sites in Missouri. The J-turn design resulted in a 34.8% reduction in crash frequency for all crashes and a 53.7% reduction in crash frequency for all injury and fatal crashes. Both reductions were significant at the 95% confidence level. Annual disabling injury crashes and minor injury crashes decreased by 86% and 50%, respectively. None of the five sites exhibited a fatal crash following J-turn implementation. This five-site analysis showed that annual right angle crashes decreased from 6.3 to 1.3, a 80% reduction. One of the most severe crash types, the left turn, right angle crash, was completely eliminated by the J-turn. One conflict measure, average time to collision, was found to be four times higher at the J-turn site compared to the control TWSC site among minor road turning vehicles, indicating greater safety at the J-turn site. The average wait time at the J-turn site was half the wait time at the control site, while the average travel time at the J-turn site was approximately one minute greater than at the TWSC site. When the public was surveyed regarding trip time perceptions resulting from the J-turn, the majority said there was no adverse effect. A high percentage of minor road left turning and through movements at the J-turn site merged into the travel lanes within the first 400 feet of the acceleration lane. Public opinion regarding the J-turn at US 63 and Deer Park Rd was mixed. Frequent concerns raised by respondents included difficulty merging following the U-turn, improper use of acceleration and deceleration lanes, insufficient U-turn radius to accommodate large vehicles, and driver confusion.

Study Citation: Edara, P., C. Sun, and S. Breslow. "Evaluation of J-turn Intersection Design Performance in Missouri". Missouri Department of Transportation, December 2013.


CMFs Associated With This Study

Category: Intersection geometry

Countermeasure: Install J-Turn intersection

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.65234.83 StarsAllAllPrincipal Arterial Other Freeways and ExpresswaysRural
0.46353.72 StarsAllA,B,CPrincipal Arterial Other Freeways and ExpresswaysRural
0.57432 StarsAllOPrincipal Arterial Other Freeways and ExpresswaysRural
0.5502 StarsAllBPrincipal Arterial Other Freeways and ExpresswaysRural
0.14862 StarsAllAPrincipal Arterial Other Freeways and ExpresswaysRural
01002 StarsAllKPrincipal Arterial Other Freeways and ExpresswaysRural
0.2802 StarsAngleAllPrincipal Arterial Other Freeways and ExpresswaysRural
01002 StarsLeft turnAllPrincipal Arterial Other Freeways and ExpresswaysRural
0.41258.82 StarsOtherAllPrincipal Arterial Other Freeways and ExpresswaysRural
0.41258.82 StarsRear endAllPrincipal Arterial Other Freeways and ExpresswaysRural