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Roundabouts point the way to safer, less-congested intersections
A roundabout at an intersection in Maplewood, Minnesota.
Roundabouts—a type of circular intersection used in place of stop signs or traffic signals —can offer many benefits. Studies show that the numbers of crashes and serious injuries plunge when roundabouts are installed, and congestion, fuel consumption, and emissions also fall significantly. So why don’t we see more of them in the United States, and what’s needed to spur their use?
Speakers shared their ideas at the Minnesota Roundabouts Conference, held April 5 and 6 in Brooklyn Center. It was sponsored by Mn/DOT and hosted by the Center for Transportation Studies, which houses Minnesota LTAP. Paul Stine of Mn/DOT was the conference organizer.
The conference, attended by more than 300 people from across the country, opened with remarks by Mn/DOT deputy commissioner Doug Differt. Roundabouts are a promising approach, he said, and might serve as another tool in the state’s Toward Zero Deaths (TZD) toolbox. In just the last few years in Minnesota, 16 roundabouts have been built, 7 are under construction, 9 in design, 4 planned, and 14 in discussion, he reported.
Next, Susan Ferguson of the Insurance Institute for Highway Safety (IIHS) presented “The Case for Roundabouts: What the Research Shows.” Calling roundabouts “an important addition to intersection planning,” Ferguson began by explaining how the approach improves safety. In roundabouts, all vehicles travel in the same direction at low speeds (15 to 20 mph), eliminating the potential for serious collisions. “Broadside crashes pretty much go away,” Ferguson said.
In contrast, signalized intersections are often built on wide streets with long crossing distances in an attempt to reduce congestion and delays. This sort of intersection, however, can be a major contributor to crashes and injuries, as drivers often stop abruptly at red lights or speed up to cross on yellow.
These views were borne out in the Institute’s 2001 study of 23 U.S. sites, which found that converting intersections from signals or stop signs to roundabouts reduced injury crashes by 80 percent and all crashes by 40 percent. Roundabouts are also generally safer for pedestrians, Ferguson said. (The blind, for example, fare better at signalized intersections.)
Though the number of roundabouts in the United States is still small—roughly 2,000—it is growing. In comparison, France has an estimated 20,000, Australia 15,000, and the United Kingdom 10,000. “Roundabouts are very simple when you get used to them,” Ferguson said, and can be used in settings ranging from rural areas to complicated urban ones.
The problem of intersection safety is widespread. Ferguson noted that more than 2.5 million crashes occurred at U.S. intersections in 2003, with 8,659 fatal crashes. These represent 41 percent of all crashes, 46 percent of all injury crashes, and 23 percent of all fatal crashes. “Roundabouts can help address these problems,” she said.
Despite their promise, roundabouts face several impediments. First, they are relatively new in the United States, so there has been some reluctance to apply them. Local residents and elected officials may oppose them. Also, questions exist about the relevance of international research and design practices to U.S. experience.
To help overcome these obstacles, Ferguson’s organization has conducted research in a number of areas in recent years. Studies reported significant improvements in traffic flow following conversion to roundabouts: vehicle delays fell 13-23 percent in one project, an average 65 percent in another, and an average 89 percent in a third. By improving traffic flow, roundabouts also decrease fuel consumption—by about 30 percent—and vehicle emissions by 20 to 40 percent.
Drivers’ opinions change quickly when they become more familiar with roundabouts. One study found that the number of drivers who support roundabouts rose from 36 percent before construction to 70 percent a year later. “Don’t be put off by opposition,” Ferguson said. “Residents may just need education.”
Ferguson closed her remarks with a summary of other benefits. Roundabouts eliminate the maintenance and electricity costs associated with traffic signals (approximately $3,000 per year). The central island provides an opportunity for landscaping and aesthetic improvements, and acts as a mid-crossing haven for pedestrians. Finally, roundabouts require fewer traffic lanes than traditional intersections to accommodate the same amount of traffic, thus requiring fewer property takings.
For more information: www.iihs.org/research/qanda/roundabouts.html.
Minnesota examples
Several Minnesotans were on hand to share their experiences with roundabouts. Chuck Ahl, Maplewood city engineer, said his city’s first use of roundabouts ignited some controversy at a public hearing. “It was a huge issue at the end,” he said.
The opposition was based on a number of factors, Ahl said. First is unfamiliarity: residents don’t know how to use roundabouts and go out of their way to avoid them. Like many Minnesotans, the area’s drivers aren’t very good at yielding and merging. They also think roundabouts cost more than signals (which is false) and that landscaping will reduce visibility, particularly of oncoming traffic.
Now that the roundabouts are in operation, however, the view of them is quite positive. Traffic flows better and the number of accidents has fallen. “Local businesses think they’re the greatest thing and want more,” Ahl said. A survey of city council members and fire, police, and public works maintenance staff found support to build more of them.
One of the questions Ahl often hears is about snowplowing. “Maintenance is relatively straightforward,” he reported, “and is not a problem for maintenance staff.” The truck speed is too slow to throw snow, however, so snow may have to be hauled in a large storm (to date, this hasn’t been needed). Street sweeping has been difficult under traffic, Ahl added.
David Thomalla, Maplewood Police chief, added that his staff sees fewer crashes as people get more comfortable with roundabouts. Only one personal injury crash has occurred since the first roundabout opened, in contrast to a number of serious crashes at the previous stop sign.
Bill Killian, a Richfield city council member, discussed the process used to choose a roundabout for 66th Street and Portland Avenue. In 2001, the signalized intersection was ranked the worst by Hennepin County for number of crashes, severity, cost, and crash rate.
The Richfield Transportation Commission led a one-year study of the intersection. With input from the neighborhood, the commission recommended a two-lane roundabout to the city council. Of all the options, the two-lane roundabout will provide the shortest traffic delays, best safety improvement, and most access for businesses. The roundabout is also coming in at the low end of the budget because of fewer takings and lower construction costs. “It’s win-win-win-win,” Killian said.
Cory Slagle of Washington County said a successful public education campaign should start early and follow a strategic communications plan. A large audience—local, county-wide, regional—needs to be informed. Target audiences include residents, businesses, schools, public safety, trucking firms, and commuters.
Slagle also suggested key messages to share in the campaign: what a modern roundabout is, how they work, how to drive around them, and their benefits.
Bernie Arseneau of Mn/DOT’s Office of Traffic, Security, and Operations said roundabouts fit into the overall plan of making transportation systems safer through the state’s Comprehensive Highway Safety Program and the TZD program. (TZD is a multipartner effort including CTS and Minnesota LTAP; see www.tzd.state.mn.us to learn more.)
—Pamela Snopl, LTAP Editor
What exactly is a roundabout?
Mark Doctor of the FHWA Resource Center in Atlanta said there can be some confusion about just what a roundabout is. The Manual on Uniform Traffic Control Devices (MUTCD) defines them as follows:
A circular intersection with yield control of all entering traffic, channelized approaches, and appropriate geometric curvature, such that travel speeds on the circulatory roadway are typically less than 50 km/h (30 mph).
Photo reprinted with permission of the Kansas DOT.
Elements of a roundabout include a circulatory roadway, a central island, a truck apron (to allow wider vehicles), a splitter island, and a deflected path (see below). Vehicles yield at entry (or in other words, a vehicle in the roundabout has the right of way) and are deflected counterclockwise around a center island at an appropriate speed.
It is important to remember, Doctor said, that roundabouts are a subset of circular intersections. “A large part of the negative perception of the public is the experience in the East Coast with large traffic circles,” he said. Rotaries such as Dupont Circle in Washington, D.C., are not roundabouts, nor are traffic-calming circles. “This is an important message to convey to the public,” he said.
The FHWA hopes to see all states progressing with roundabouts, Doctor noted.
For more information, see the FHWA’s Roundabouts: An Informational Guide; the MUTCD; or the AASHTO Policy on Geometric Design (the “Green Book”).