With 16 roundabouts completed, Dublin is looking toward its most ambitious intersection yet.
Plans are in motion for a roundabout at state Route 161 and Riverside Drive, an option Dublin Engineer Paul Hammersmith called the best for the heavily traveled intersection.
An analysis of the intersection was done a few years ago that found keeping a traffic signal there and maintaining "the same level of service required significant modifications to the bridge over the Scioto River," Hammersmith said. "We would have to widen the bridge to provide needed turn lanes.
A roundabout would provide a good level of service, improve safety and eliminate the high costs of adding to the bridge, Hammersmith said.
"With a roundabout the bridge can stay as it is," he said.
Dublin has installed roundabouts at busy intersections in the past.
The Avery-Muirfield Drive/Post Road and state Route 161/Industrial Parkway roundabouts carry a lot of traffic daily, Hammersmith said.
"This probably will be the busiest," he said of the planned Riverside Drive/state Route 161 roundabout.
The new multi-lane roundabout is expected to cost $4 million and construction is slated for 2015.
"Generally speaking there will be two lanes on one side and three lanes on another," Hammersmith said of plans. "There will be three lanes on the east side - two for the roundabout and one for an additional turning movement."
The bypass that takes traffic south on Riverside Drive under the state Route 161 bridge will remain, Hammersmith said.
With several roundabouts under the city's belt, Hammersmith said he expects the one at Riverside Drive and state Route 161 to improve safety and traffic flow, as others have around the city.
"I think what we're seeing city wide is greater efficiency as far as service and moving traffic," he said.
"A roundabout has continuous flow. It's always filling in the gaps and you don't have a delay you'd have with a traffic signal or four-way stop ... . With a roundabout all users can use the intersection when it's available to them.
"That's quite simply yielding to the left."
The city has also seen traffic crashes decrease at intersections where roundabouts have been installed, Hammersmith said.
A three year study between 2010 and 2012 found 44 crashes at the Riverside Drive and state Route 161 intersection.
"Generally speaking at a signalized intersection you'll have more injury-related crashes than we do at roundabouts or a four-way stop intersection," he said.
The severity of crashes has also decreased after roundabouts in Dublin have been installed.
People tend to slow down for roundabouts as opposed to traffic signals, Hammersmith said.
"Speed causes accidents to be more severe," he said.
City surveys have found most Dublin residents like the roundabouts and that, paired with making safer, more efficient intersections, makes them a winner for Dublin.
"What roundabouts have done for us is they improved intersection safety greatly," Hammersmith said.
"They reduced crash rates and significantly reduced injury crash rates," he said.
"Secondly they increase levels of service... We've also ended up with a quieter intersection.
"That's one of the comments I've heard," Hammersmith said.
"Secondly when you don't have idling vehicles you get improved air quality."