Improving safety of two-lane roundabouts

roundaboutWhile two-lane roundabouts almost always reduce fatal and severe crashes, they can also lead to a substantial increase in minor crashes. To help combat this problem, researchers with the Roadway Safety Institute are investigating solutions for reducing crashes at two-lane urban roundabouts.

The research, funded by the Minnesota Department of Transportation, began in 2011 with a troublesome two-lane roundabout in Richfield, Minnesota. Following the roundabout’s construction, the number of property-damage crashes increased substantially at the site. Experts at the Minnesota Traffic Observatory (MTO) were brought in to make improvements and gauge their effectiveness with a before-and-after study.

“With the assistance of local and national roundabout experts, we made a number of changes in the signs and lane markings,” says MTO director John Hourdos. Changes included adding lane designation signs upstream of the approach, removing fishhook-style arrows, extending the solid lane line upstream of the roundabout, eliminating the solid-and-skip lines, lowering signs to improve visibility, and adding crosswalk signs on the islands.

The effects of these changes were documented with a 360-degree camera mounted in the center of the roundabout. Based on collected data, the researchers concluded that a number of the changes had a significant, positive long-term effect.

“After the changes, lane-change violations decreased 20 percent, turn violations dropped more than 40 percent, and lefts from the outer lane—the most severe violation—were reduced 45 percent,” Hourdos says. “One early clue that led us to believe that the changes were significant is that we immediately saw a 53 percent improvement in selecting the correct lane—which was sustained one year later.”

Following the success of this project, researchers wanted to extend the investigation to more roundabouts with different designs. In a new project, funded by the Minnesota Local Road Research Board, the research team is accomplishing this by studying four additional two-lane roundabouts in Minnesota that vary greatly in age, driving conditions, and built environment. Researchers have collected before-and-after data at all four roundabouts. Video analysis is currently under way, with results expected later this year. The project also includes the use of automated violation detection for the video analysis.

Based on the results of the data analysis, researchers will develop guidance for Minnesota county and municipal engineers seeking to improve safety and reduce property damage crashes at their urban two-lane roundabouts. Once this project is complete, researchers hope results may pave the way for a larger, multi-state study.

Posted in Safety, Traffic operations, Transportation research

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