Modern Roundabouts: Safe. Efficient. Attractive.

Brian Armstrong, P.E., PTOE
Senior Project Manager
Bartlett & West
Topeka, Kansas
Presenter, 2007 APWA Congress

The popular online information source Wikipedia provides definitions for eight different types of roundabouts, everything from the "Gyratory" to the "Magic" roundabout. So some confusion is natural. This may account for the resistance city engineers sometimes confront when proposing roundabouts for local intersection solutions. While many citizens find change of any sort potentially threatening, studies have nevertheless shown modern roundabouts are an unmatched design solution for safe, efficient and attractive intersections.

"Driving Design—Making Roundabouts Work," a presentation to be given at the 2007 APWA Congress by Brian Armstrong, P.E., PTOE, of Bartlett & West, and Tim Green, P.E., City Engineer for the City of Lenexa, examines a number of practical lessons learned designing modern roundabouts for a variety of applications. Utilizing a number of projects as case studies, Brian and Tim will explain how they've dealt with a variety of issues—some technical and some not—and the lessons they learned that helped shape their thinking on future projects.

Their first piece of advice: If roundabouts are a new feature in your city, it would be wise to proceed cautiously and with a clear plan in mind to win the hearts and minds of constituents who may suffer from a number of misconceptions about this relatively new tool in traffic control.

That's right, new. Today's modern roundabout bears little relationship to the large, admittedly scary rotaries built in Europe and the eastern United States during the first half of the twentieth century. When preparing citizens for a discussion of roundabouts, this is a critical point to make. While many citizens find change of any sort potentially threatening, studies have nevertheless shown that modern roundabouts are an unmatched design solution for safe, efficient and attractive intersections. Conveying this message is the key to instituting a successful roundabout program in your community. A study by the Insurance Institute for Highway Safety (IIHS) compared public opinion before and after a roundabout was installed. It found that once citizens experience a roundabout, respondents in the "strongly oppose" category fell from 41 percent to just 15 percent, the "strongly favor" category doubled from 16 percent to 32 percent, and the "somewhat favor" category doubled from 15 percent to 31 percent. Public education can go a long way toward reducing resistance.

Some public confusion on the subject is understandable. At first glance, there might appear to be little difference between an effective, modern roundabout, its smaller cousin the traffic-calming turning circle, and the large, often dangerous rotaries of the past. The differences, however, are real, significant and important to understand.

The rotaries of yesteryear, for example, were generally much larger than modern roundabouts, with vehicles often moving at high rates of speed within the circle. Drivers within the circle were to yield right-of-way to cars entering the rotary, causing congestion, sudden stops and potentially dangerous maneuvering within the circle. Many of these inefficient designs were ripped out in the latter half of the twentieth century to be replaced by stop control or signaled intersections, or in some cases by smaller, safer, modern roundabouts.

Photo 1: This roundabout at 41st Street and Wannamaker Road in Topeka, Kansas, contains most of the key features of a modern roundabout.

Roundabouts are also frequently confused with turning circles. Though they may look similar, turning circles are generally smaller tools used to calm traffic on residential streets. Their purpose is to slow—or discourage altogether—through traffic in the neighborhood. Frequently they fit within the existing intersection, creating an obstacle with much the same effect as speed humps or bulb-outs. Some allow left-turning cars to pass to the left of the central island rather than going around it.

Modern roundabouts utilize yield control at all entries, and employ geometric features like splitter islands to promote slow and consistent speeds for entering vehicles. Key features of a modern roundabout include the following:

  • A raised central island in the center of the roundabout with traffic circulating around it.
  • Splitter islands to separate entering from exiting traffic and to deflect and slow traffic. These also prevent drivers from making left turns entering the roundabout rather than going around it. (Most of the key modern roundabout features can be seen in Photo 1.)
  • A circular roadway of one or more lanes to move traffic in a counterclockwise path around the central island.
  • Right-of-way yielded by traffic entering the roundabout.
  • Pedestrian crossings to facilitate foot or bike traffic.
  • Aesthetic elements like landscaping, fountains or public art in the central island. Low ground cover should be used in the outer margins of the central island to assure unobstructed sight distance.

In addition to questions of public perception, Brian and Tim will discuss the following issues:

  • The importance of up-front coordination with City and State to verify need and select location.
  • The value of completing preliminary design before establishing project budget
  • The benefit of considering whether the roundabout should be constructed for the ultimate development scenario or for an initial traffic scenario with the ability to expand with development in the future. (A good example of this can be seen in Photo 2.)
  • What to consider with multiple roundabouts in a corridor setting.
  • The importance of reviews early in the design process.
  • A host of technical considerations, including pavement cracking and joint-spacing, drainable bases and other lessons learned.

Photo 2: This roundabout at Sixth Street and Wannamaker Road in Topeka, Kansas, was built to accommodate the area's ultimate development scenario.

So why should a city consider roundabouts?

Safety is one reason. Consider an IIHS study which reported a 90 percent reduction in fatal crashes, coupled with a 76 percent reduction in injury crashes. Roundabouts reduce potential vehicle conflict points from 32 for a stop control or signalized intersection to eight. Traffic is deflected entering a roundabout, reducing the potential for full-impact collisions. Finally, speed is reduced, lessening the severity of any accidents that do occur.

What's more, roundabouts can handle traffic flows more efficiently, reducing delays because drivers do not have to wait for a traffic signal to cycle. Not only do drivers get to their destinations more quickly, they save gasoline and reduce pollution as well.

Reduced maintenance and operational costs over signals are additional pluses for public works departments.

Add to this the aesthetic potential of roundabouts to enhance the driving experience and you can see why modern roundabouts are becoming an intersection option of choice in many communities.

Brian Armstrong and Tim Green's presentation at the 2007 APWA Congress will take place on Sunday, September 9, at 8:30 a.m. Brian Armstrong can be reached at (785) 272-2252 or brian.armstrong@bartwest.com; Tim Green can be reached at (913) 477-7680 or tgreen@ci.lenexa.ks.us.