Roundabouts

Roundabouts are an effective tool for reducing congestion and traffic crash injuries. Roundabouts are becoming more common on our roadways, yet they are often misunderstood as dangerous. While new roundabouts can involve a short adjustment period as drivers learn a new traffic pattern, their long-term purpose is clear: slower speeds and safer roads for everyone. In fact, roundabouts offer significant safety benefits:

• When a traditional two-way stop intersection is replaced by a roundabout, fatal and injury crashes are reduced by 82%¹.
• When a signalized intersection is replaced, fatal and injury crashes are reduced by 78%².

Roundabout Quick Tips

• When approaching a roundabout, slow down and yield to traffic in all lanes of the roundabout.
• Do not change lanes inside a roundabout. Look for signage and choose your lane prior to entering the roundabout.
• Use your signal when exiting a roundabout.
• Yield to pedestrians and cyclists when entering and exiting a roundabout.

Roundabout benefits

• They are able to move traffic more efficiently than traditional intersections while reducing the number of crashes resulting in deaths and serious injuries.
• More environmentally compatible and provide pleasing aesthetics.
• Roundabouts make navigation easier for pedestrians and bicyclists, when designed correctly, due to lower vehicle speeds and fewer conflict points.
• Roundabouts have fewer conflict points than traditional intersections and result in lower severity crashes.

Source: Next STL

Case Study: Washtenaw County Road Commission

Washtenaw County Road Commission (WCRC) conducts annual monitoring of intersections, primarily on two-lane high-speed county roads. This monitoring program includes evaluation of potential candidates for roundabouts or traffic signals based of crash history and delay at each location. There are now over 30 roundabouts in Washtenaw County. The first roundabout in Washtenaw County was installed in 2003. Since then, the number of intersection crashes resulting in any injury has decreased by nearly 40% across the county. WCRC found that roundabouts with a diameter of 100 to 110 feet have the best performance in terms of safety and operations. WCRC continues to monitor locations with field visits and crash reports. More information on roundabouts in Washtenaw County can be found on the WCRC website.

Case Study: Road Commission for Oakland County

The Road Commission for Oakland County (RCOC) is one of the agencies leading the way in the use of roundabouts – which can increase capacity (the amount of traffic that can flow through) from 30-50% and help to ease traffic congestion. One example is the roundabout at M-5/Pontiac Trail/Martin Parkway.

This is a high-volume intersection, where a state highway dead-ends into a county road. We actually built this roundabout, in part, as a way to deal with all the serious injury/fatality crashes that were occurring at the intersection when it was signalized. People would come cruising down M-5 at 60-plus miles an hour and not be able to stop at the intersection. While that remains a problem today, the design of the roundabout helps to slow them down and we are, at least, having no fatalities and few serious injury crashes. So, this roundabout has accomplished what it was intended to do. Immediately following our ribboncutting ceremony to open that roundabout, an Oakland County Sheriff’s deputy pulled a couple of us aside and thanked us for building the roundabout. He said he was getting very tired of having to respond to fatalities at the previous traffic signal at the intersection. There have not been any fatalities there since the roundabout was built in 2011.

-Craig Bryson, Senior Communications Manager, RCOC

More Resources

• U.S. Department of Transportation Federal Highway Administration shares more information on roundabouts.