In 1992, the Maryland DOT State Highway Administration (MDOT SHA) formed a Roundabout Task Force to identify an intersection with traffic volumes that didn’t meet signalization requirements yet had a high crash rate. MD 94 (Woodbine Road) at MD 144 (Frederick Road) in Lisbon quickly gained attention. Despite a flashing beacon and stop signs, 33 crashes occurred from 1989 to 1992. Almost half – 15 – caused injuries. An estimated 5,500 vehicles traveled the route daily.
Traffic engineers created a temporary roundabout using line striping and rumble strips so they could evaluate the configuration’s effectiveness. The accident rate fell and they made the installation permanent. Crashes have decreased by 73% since then and traffic flows mores smoothly.
“As roads get busier and growth continues, roundabouts are increasingly becoming a go-to solution to solve complex highway issues,” says MDOT SHA Administrator Gregory Slater. “Roundabouts have been proven to improve safety by eliminating vehicle conflicts.”
Roundabouts came to the U.S. from the U.K. in 1905 in New York City. The design maintains continuous traffic flow at a safe speed, prevents the perpendicular collisions common to intersections, and lowers costs by eliminating the need to buy and maintain traffic signals.
Before the Lisbon roundabout’s success, there were public hearings whenever they agency proposed a roundabout. Now it’s not unusual for residents to ask about installing roundabouts at MDOT SHA-maintained roads in their communities. An online tutorial shows drivers, bicyclists, and pedestrians how to navigate roundabouts. Design has evolved to accommodate larger vehicles, farm equipment, and trucks.
In feasibility studies, engineers consider all alternatives -- all-way stop, signalization, and roundabout – and analyze service levels, queue levels, and crash reduction rates for each. “In most cases, the decision comes down to a signal or a roundabout,” says MDOT SHA Roundabout Coordinator Mike Niederhauser. “If all things are relatively equal, the roundabout typically wins out. They’re key to our traffic safety and congestion relief toolbox.”
Accidents at the state’s first eight roundabouts have fallen 64% and crash-related injuries have fallen 83%. There have been no fatal crashes. MDOT SHA manages 88 of the nearly 200 roundabouts in the state.
