MnDOT traffic engineers are increasingly installing J-turn intersections on high-speed, multilane expressways to limit potential crash points. An analysis of crash data from intersections before and after the installation of J-turns demonstrated significant safety benefits from this alternative design. MnDOT researchers also explored crash history differences among J-turn intersections with varying characteristics. Consistent with the results from a previous study, this analysis found a clear decrease in fatal and other serious crashes after a J-turn was installed.
Traditional intersections on highways can present multiple points where crashes could occur between vehicles crossing paths. Having to traverse fast-moving lanes of traffic to get to opposing lanes creates the risk of right-angle—or T-bone—crashes, which can be severe.
Intersection designs intended to improve safety include traffic signals, which often do not protect against angle crashes, and grade changes, which can be cost-prohibitive. A J-turn—or restricted crossing U-turn—offers a lower-cost, effective solution in which points where vehicle paths may cross are limited.
In a previous study conducted in 2021, MnDOT compared crash histories since 2010 at 49 intersections before and after the installation of J-turns and at intersections without J-turns. Results showed statistically significant decreases in fatal and serious injury crashes. Since the data collection from that study, additional J-turns have been installed in Minnesota.
By the end of 2023, Minnesota had 96 J-turns on state roadways and more planned or under construction. While interest among traffic safety professionals remains high, public opinion is mixed. MnDOT wanted to analyze the additional data and explore questions that have arisen regarding various aspects of J-turn design.
What Did We Do?
Adjusting for traffic volume, MnDOT compared all crash data, including fatal and serious injury, angle, rear-end and sideswipe crashes, through 2022 from intersections before and after J-turns were installed. While 83 J-turns existed at the time of the research, insufficient data and other conditions at 29 locations limited the analysis to data from the 54 remaining J-turns, some with over 10 years of data.
Before-after analyses of 38 J-turn intersections and 61 control intersections with similar characteristics, and of J-turn locations and rural signalized intersections or low-volume interchanges provided a comparison between intersection types.
“Given the number of J-turns in Minnesota, these results revealing significant benefits are what we want to see. Also, we hope other states can benefit from these findings,” said Maxwell Moreland, traffic safety crash data engineer, MnDOT Office of Traffic Engineering.
The study also included a review of the characteristics of a J-turn, which offer drivers from a minor road a safer crossing of a major road.
In a J-turn, instead of crossing multiple lanes of traffic as in a traditional intersection, drivers turn right onto the main road, merge into the left lane and make a U-turn. Then they either continue traveling in that direction, as if they made a left turn from the minor road, or turn right onto the minor road, as if they had gone straight across the major road.
J-turns may be installed in conjunction with a channelized left-turn lane on the main road.
Additional analyses examined the effects of different design aspects of J-turn intersections:
- Main roads with varying traffic volumes.
- Presence or absence of mainline left-turn lanes.
- Different entry points into the U-turn lane.
- Varying distances between the U-turn and the side road.
What Did We Learn?
Consistent with the results of previous research, intersections converted to J-turns demonstrated a significant decrease in fatal and serious injury crashes, other injury crashes and angle crashes.
While rear-end crashes saw a significant increase, the majority resulted in property damage only. The installation of J-turns resulted in fewer high-severity crashes, demonstrating that the design is an effective safety treatment.
Compared to signalized intersections, J-turns had fewer angle, rear end and intersection-related crashes. Similarly, compared to rural signalized and low-volume interchanges, J-turn intersections showed lower overall and injury crash rates.
While intersections with all levels of main road traffic volumes demonstrated reductions in serious crashes when J-turns were installed, main roads with average annual daily traffic of less than 10,000 vehicles saw the biggest benefit.
What’s Next?
Results from this study and previous research indicate the safety benefits of J-turns. MnDOT is currently working on a technical memorandum for J-turn implementation. The guidelines and expectations contained in the memo will consider the substantial safety benefits of J-turns for reducing severe crashes.
Crossroads 