Checking the progress of the modern designs reveals they now number in the thousands across the United States. Maybe they're right for your next intersection makeover?

The occasion passed this year without note–most people being unaware–and probably the dozens of high-profile stories about infrastructure funding and autonomous vehicles would have eclipsed the event anyway. Despite the lack of fanfare, however, roundabouts in the United States recently experienced a twentieth anniversary, more or less.

Although there is no exact date to pinpoint, national efforts to establish modern roundabouts as an accepted intersection design can be traced back about 20 years. As documented in the National Cooperative Highway Research Program (NCHRP) Synthesis 488 Roundabout Practices, over the course of the past two decades or more, roundabouts have grown from a few sprinkled around the United States to several thousand–with at least one in every State, and some with hundreds.

Experts in the field estimate that the United States now has nearly 4,500 modern roundabouts, meaning the number has nearly doubled over the past 10 years. Compared to countries such as France or the United Kingdom, on the basis of roundabouts to population rate, the United States is still lagging.

Nevertheless, several recently achieved milestones bode well for closing the gap with the Nation’s international peers. In 2016, Carmel, IN, constructed the city’s 100th roundabout. The Wisconsin Department of Transportation finished constructing the first pair of roundabouts with three lanes circulating at the U.S. 41 and WIS 29 interchange in Green Bay and a total of 40 roundabouts along the U.S. 41 corridor in the State’s northeastern region. And in 2017, Yosemite National Park in California and Arches National Park in Utah are constructing the third and fourth roundabouts, respectively, within the National Park Service’s roadway network.

“Equally notable is that roundabouts are now widely accepted as more than just a solution for traffic safety, but also for their potential as a proven solution for congestion relief and management,” says Rob Ritter, acting director of safety design for the Federal Highway Administration. “They’re also accepted as a keystone of community walking and biking efforts, and as a catalyst for establishing policies for selecting types of intersections predicated on performance-based metrics and outcomes.”

The long-term progress has been slow but steady. It now shows signs of accelerating, thanks to persistence and perseverance by the practitioners on the front lines.

These are their stories.

Stories from the Field

Where a State or local agency introduces roundabouts for the first time, regardless of motivation, controversy is almost sure to follow. After all, even if roundabouts are familiar to the intersection designer or traffic engineer, they may still be new in a given community. That they are circular instead of orthogonal (right-angle), and rely on yielding instead of binary stop-and-go traffic signals or stop signs, tends to make people feel uneasy at first. Another frequent concern that people express when discussing roundabouts is how to choose the right exit to reach their destination.

Roundabouts Articles in Public Roads Over the years, Public Roads has tracked the implementation of roundabouts in the United States. The first feature article in 1995 established the early context and predated the Roundabouts Informational Guide (FHWA-RD-00-068) published in the year 2000, while subsequent articles focused on lessons learned along the way, including the adaptation of roundabouts to different contexts such as at interchanges, junctions with recreational paths, roadway corridor solutions, and scaled-down versions known as mini-roundabouts.

An agency proposing roundabouts in a community for the first time must be prepared to address these anxieties and other concerns. A number of strategies are available, beyond the typical informational meeting on a project. FHWA documented several approaches in a series of case studies known as the “Roundabouts Outreach and Education Toolbox.” The overarching lesson from these case studies is that a proactive and persistent approach is often successful, as seen in the cases below.

California. An example from Fresno County, CA, illustrates a classic case of a roundabout proposed as a spot safety improvement. Over a 3-year period, the intersection of State Route 145 and Jensen Avenue near the city of Kerman experienced 10 broadside crashes. The incidents happened despite SR–145 being only a modestly busy highway with roughly 700 vehicles entering the intersection on weekdays during peak hours.

To reduce the number of crashes resulting in injuries to drivers and occupants, the California Department of Transportation (Caltrans) targeted this intersection for conversion from a stop-controlled intersection to a single-lane roundabout. The analysis conducted by Caltrans District 6 clearly demonstrated that a roundabout was the optimal solution for this intersection, with the potential to greatly enhance safety performance while also satisfying goals for mobility and efficiency.

This segment of SR–145, however, is in a heavily agricultural area of the State, meaning that nearby farmers move large equipment and trucks through the intersection on a regular basis. To help address the concerns of the farming stakeholders, Caltrans District 6 organized what the agency and other jurisdictions call a “roundabout rodeo.” The district held the event in a parking lot where the public could drive through a mock roundabout replicating the proposed design of a roughly 150-foot (46-meter)-diameter roundabout. (For a video, see www.youtube.com/watch?v=2h3CirwT9xk).

This proof-of-concept demonstration alleviated most of the concerns of the agriculture and trucking industries, helped the project move forward, and laid the groundwork for future cooperative efforts with industry partners on a statewide scale. Subsequently, Caltrans consulted with the California Farm Bureau Federation and the California Trucking Association to solicit feedback to be incorporated on future roundabout designs across the State. Not only did this project catalyze collaboration between Caltrans and key stakeholders, it ultimately proved successful in its aim to improve safety. In observing the operation of the roundabout since construction was completed in 2014, Caltrans has found that the roundabout has eliminated the broadside and injury crashes experienced in the original intersection.

Georgia. On the Nation’s opposite shore, along one of the most congested corridors in the country, the Georgia Department of Transportation (GDOT) built its first interchange with roundabouts in 2016 under a design-build contract. The agency converted conventional signalized ramp terminal intersections to single-lane roundabouts at the diamond interchange of I–285 with Riverside Drive in Sandy Springs. GDOT constructed the roundabouts using an innovative design-build method to expedite delivery.

The reasons for choosing roundabouts were twofold, and closely related. At this milepost, I–285 in Fulton County carries approximately 219,000 vehicles per day and Riverside Drive just over 4,000 vehicles daily. The conventional signalized intersections at the interchange experienced both operational and safety issues that needed to be addressed.

On most weekdays at afternoon peak hours, the exit ramp queues would reach the freeway mainline, creating safety concerns. After GDOT converted the two existing signalized ramp terminals to single-lane roundabouts, the afternoon peak delays were significantly reduced. A study done prior to the project estimated delays going from 234 seconds per vehicle (signal) to 23 seconds per vehicle (roundabout) at the eastbound ramp intersection, and from 111 seconds per vehicle (signal) to 12 seconds per vehicle (roundabout) at the westbound ramp intersection. Reducing the chronic intersection congestion has helped to resolve the queuing on the ramps.

The experience at the I–285/Riverside Drive interchange is just Georgia’s latest roundabouts-related success. Scott Zehngraff, assistant State traffic engineer at GDOT, continues to look for opportunities where roundabouts can be implemented to improve intersection safety and reduce congestion. He reports that GDOT installed its first roundabout on the State highway system in 2004, added one more in 2007, and were up to five by 2012. This is when the pace really picked up, with 17 more roundabouts completed since 2013 and 16 under construction in 2016–2017.

As Zehngraff explains, “It took us a while to get going, but now that we clearly know the benefits of roundabouts, we are making full use of their demonstrated safety and operational benefits. In the past, we had to work hard to convince local governments that a roundabout is the most appropriate solution for a particular intersection; now, however, we are seeing jurisdictions throughout the State taking the lead in pursuing roundabouts to fix safety and operational issues in their communities.”

Michigan. The Washtenaw County Road Commission (WCRC) in Michigan has been constructing roundabouts for several years and recently added mini-roundabouts to its portfolio. The county now has just shy of two dozen roundabouts of varying sizes and lane configurations, and the trend to build roundabouts is expected to continue, even while the approach has evolved.

Mark McCulloch, senior project manager at WCRC, says, “We’ve had tremendous success with roundabouts in terms of reducing severe crashes and eliminating congestion, but we’re always looking for ways to save money and time when delivering our projects. Mini-roundabouts–or as we call them in our area, urban compact roundabouts–have much smaller footprints, so they cost less and have fewer right-of-way impacts, meaning we can build more of them more quickly, providing our communities with the safety and operational benefits sooner.”

The multifold success of mini-roundabouts in Washtenaw County–safer, cheaper, sooner–has led the WCRC to emphasize “right-sizing” roundabouts going forward. The goal is to balance the immediate need to improve safety and traffic flow with future capacity demands.

Although the overall experience with roundabouts in Washtenaw County has been quite successful, it has not been without a few bumps along the way. In some instances, nonserious crashes increased after the roundabouts were built. After investigating the underlying causes and realizing it was largely due to driver unfamiliarity, McCulloch recruited Katie Parrish, WCRC communications coordinator, and the two set out to tackle issues related to driver education. They conducted an online survey, leveraged social media to spread the message about roundabouts, and created a public service announcement (PSA) contest involving a local high school.

The online survey attracted more than 4,300 respondents and provided valuable insight about how people in the area, including law enforcement, perceived how roundabouts are supposed to work. This insight helped WCRC craft targeted messages when its representatives spoke at public meetings or answered questions in the community.

A social media product is the catchy “Yield Is Your Shield” tagline, which is now a Twitter hashtag (#yieldisyourshield) used to spread educational messages about driving through roundabouts.

McCulloch and Parrish are especially proud of the PSA contest held in partnership with Saline High School, which produced a YouTube^™ video that has been viewed more than 10,000 times.

Recent FHWA Roundabouts Research

As roundabouts became more common across a range of traffic conditions and locales, various questions emerged on how to tailor certain aspects of their design to better meet the needs of a growing number and diversity of stakeholders. FHWA sponsored a comprehensive evaluation of topics including safety performance, operational efficiency, environmental effects, freight and truck movement, and pedestrian use and accessibility. The seven volumes of reports published under the title Accelerating Roundabout Implementation in the United States represent a notable advance in the state of practice of roundabouts.

According to Parrish, “We’ve developed a multifaceted program to help educate the community on how to properly navigate a roundabout. Our goal is to educate drivers so that we can also eliminate noninjury, nuisance crashes resulting from driver confusion. Roundabouts are too valuable a tool in our toolbox to risk getting a bad reputation from preventable fender-bender collisions.”

Washington. The State of Washington has been a leader in roundabouts for more than 15 years, yet many roundabout projects still do not come easily. Even with a culture of safety and thinking outside the box, the Washington State Department of Transportation (WSDOT) finds that continually nurturing innovation and striving for well-rounded performance are still important.

From 2012 to 2016, WSDOT was faced with the challenge of replacing the Evergreen Point floating bridge on SR–520, which connects Seattle with its east side suburbs. The bridge had reached the end of its service life, and along with its replacement came previous commitments to the communities that would be directly affected. Those commitments included improving two nearby partial interchanges and providing connectivity for all modes, including a regional bicycle trail, a transit facility at Yarrow Point, and improved safety and mobility across the board.

The SR–520 project team had been considering roundabout alternatives conceptually but needed to carefully manage the expectations of various stakeholders. Therefore, the team proceeded with caution, engaging with the surrounding communities until the idea gained sufficient traction. Residents of those communities had varying degrees of understanding about how roundabouts work, especially those facilities that would have high pedestrian and bicyclist volumes.

5th International Conference on Roundabouts In May 2017, roundabout experts from around the world convened in Green Bay, WI, as the Transportation Research Board (TRB) hosted the 5th International Conference on Roundabouts. Green Bay is located in the Wisconsin Department of Transportation's (WisDOT's) northeastern region, home to dozens of roundabouts–the largest regional concentration in the State and known for several of Wisconsin's first modern roundabouts in Brown County. TRB staff and volunteers from the ANB75 Roundabouts Committee collaborated with members of the local event planning committee from WisDOT and the University of Wisconsin Traffic Operations and Safety Laboratory to deliver a stimulating program of podium presentations, poster presentations, and numerous field–based, hands–on learning opportunities and tours at nearby roundabouts. The International Conference on Roundabouts is held every 3 years and is consistently one of TRB's most popular and successful recurring midyear programs, each time attracting more than 300 researchers and practitioners from the United States and dozens of other countries. In partnership with TRB, FHWA has funded the recording and posting of the proceedings of the roundabouts conferences at http://teachamerica.com/RAB.html to foster continued technology deployment by those unable to travel to the events in person.

As the SR–520 project proceeded, an alternative emerged that involved roundabouts constructed on a bridge structure (referred to locally as a “lid”) over a freeway, creating an opportunity for the project team to draw upon internal roundabout resources and expertise in WSDOT.

Brian Walsh, WSDOT traffic design engineer and co-chair of the Transportation Research Board (TRB) Roundabout Committee, has this to say about the project: “The roundabout interchanges provided a better fit with the multimodal goals of the project that will pay dividends into the future for pedestrian and bike connectivity within the communities at these very busy interchanges. Walking through these interchanges is enjoyable, and the roundabouts help create that positive experience.”

The roundabouts-based solution succeeded in meeting the expectations of the local stakeholders. They stand today as aesthetically attractive interchanges that feature an extensive network of shared-use recreational paths and open, green space.

What’s Ahead for Roundabouts?

At the 5th International Conference on Roundabouts, one of the hot themes was the topic of Intersection Control Evaluation (ICE) policies and procedures. ICE is not a new engineering process per se; rather, it involves establishing a performance-based framework and metrics for assessing intersection types and control alternatives.

At the time of the conference, only five States–California, Indiana, Minnesota, Washington, and Wisconsin–had established ICE policies, but more States reported active efforts to implement or investigate ICE for themselves. Florida, Georgia, Nevada, and Pennsylvania indicated that their ICE policies are expected to be completed by early 2018.

The appeal of ICE is straightforward. States have recognized that ICE can complement performance-based, practical design initiatives and provide an excellent opportunity to bring explicit safety performance into the early stages of intersection decisions. The performance-based approach of ICE goes hand-in-hand with what roundabouts offer, including providing an objective, quantitative basis to inform decisions.

Caltrans Director Malcolm Dougherty notes, “Our primary concern is always with making investment decisions that optimize the safety, health, and mobility of all travelers. The findings generated by our ICE studies have supported the use of roundabouts as a sustainable, cost-effective option to improve air quality and traffic flow. Roundabouts decrease vehicle speed and significantly reduce traffic delays, environmental impacts, and the risk of collisions, as compared to side street stops or signalized intersections.”

With thousands of successful roundabouts now in operation across the United States, surely the skeptics are now few in number.

Hillary Isebrands, Ph.D., P.E., is a safety engineer with the FHWA Resource Center, Safety and Design Technical Service Team. She has a B.S., M.S., and Ph.D. in civil engineering from Iowa State University.

Jeffrey Shaw, P.E., is the intersections program manager with the FHWA Office of Safety. He has a B.S. in civil engineering from the Illinois Institute of Technology.

For more information, see http://safety.fhwa.dot.gov/intersection or contact Jeffrey Shaw at 708–283–3524 or jeffrey.shaw@dot.gov.