City engineers are paying attention to the lessons learned at the Superior Street roundabout as they design almost a dozen new roundabouts across Lincoln.
The city often peers ahead when widening a street, making the new street wide enough to handle the growing number of cars and trucks expected in 20 years. But that plan isn’t necessarily a good idea regarding roundabouts, says Thomas Shafer, design/construction manager for the Public Works and Utilities Department.
The city will make future roundabouts “right-sized for the volumes we have, with the ability to expand if the volume increases,” Shafer said. “We won’t make them bigger than they need to be.”
And future multi-lane roundabouts will be designed so the driver can’t see the entire intersection as they approach. When drivers can see the entire roundabout as they approach, they misjudge the gaps and often don’t slow down enough to be able to stop before entering a traffic lane, Shafer said.
The multi-lane roundabout at 14th and Superior streets was designed for the future. Completed in the summer of 2012, it was designed to handle the much-greater traffic load expected in the 2030s.
The new roundabout successfully reduced the time spent waiting at the intersection when controlled by traffic signals during peak drive times, but the number of accidents increased dramatically.
City officials hired MTJ Roundabout Engineering, a roundabout consulting firm, which recommended easing the complexity of the roundabout by reducing the number of lanes and installing fences to keep drivers from seeing the entire intersection as they enter.
The fixes worked. The number of accidents at the multi-lane roundabout dropped dramatically after the city shut off lanes, with just four accidents reported in October 2013 after the changes, compared with 17 accidents in the previous month.
The number of accidents, however, has never dipped below the intersection's pre-roundabout accident average, but the good news is that the severity of those accidents has decreased.
In roundabouts, most crashes involve side-swiping another car, accidents that are less costly than T-bone crashes common at traditional intersections. The average accident cost prior to the roundabout was around $5,000. In the past year, the average cost per accident has been around $2,700.
The city will design future roundabouts so the land is available to add lanes as traffic counts increase, Shafer said. You don’t want to make them too large at the beginning.
However, the city will continue to consider roundabouts for intersections across the city. Shafer said roundabouts are safer, help with handling traffic capacity at peak times and are less expensive to build.
That doesn’t mean they are the right use for every intersection. "We are going to try our best to put them in the right place," he said.
Roundabouts are planned for Coddington Avenue and West Van Dorn Street, 14th Street south of Cornhusker Highway, along Yankee Hill Road between 70th and 84th streets, at 56th Street and Yankee Hill, 14th Street and Warlick Boulevard and 66th and Fremont streets.