When I took office as mayor of Oklahoma City in 2004, my goals were similar to any other mayor’s: to improve our economy, raise our national profile, and protect our citizens. We had an intersection with safety concerns, and our planning department was pushing the idea to me and the City Council to install a traffic circle. At the time, traffic circles were new to this generation of Oklahoma City drivers, but we soon found out that they were cost-effective and most certainly safer. Ultimately, those things proved to be true for that location.
Depending on their design, traffic circles, roundabouts, and rotaries keep cars moving, reduce accidents, protect pedestrians and cyclists, and have environmental benefits, too. When they’re installed as part of a new road system or to replace an intersection that lacks stoplights, they’re cost-effective.
That experience with our traffic circle raised my awareness of the issue, after which I ran into Jim Brainard—mayor of Carmel, Indiana, from 1996 to 2024—at a U.S. Conference of Mayors event. I found out that Jim was the guru of roundabouts. Carmel, which has 100,000 residents, now has 158 roundabouts, and it will have just one traffic light left by 2026.
By the way, Jim explained to me that despite the terms often being used interchangeably, there’s a difference between traffic circles—often called rotaries—and roundabouts. Traffic circles and rotaries often have multiple lanes, sometimes with stoplights, and can lead to an increase in car accidents because of driver confusion. Think about big circles such as Dupont Circle in Washington, D.C., or New York’s Columbus Circle, which are far different from the roundabouts we’re talking about here. Roundabouts typically have one or two circular lanes that are simpler to understand and that reduce traffic fatalities.
Development during the 20th century in most cities in the Midwest revolved around cars. Part of what we’re doing now is dealing with the issues those planning decisions created. Roundabouts are part of the answer.
Safety benefits to a sprawl solution
Jim told me that he spent time in Europe and recognized the positive impact of roundabouts on traffic flow. Like many cities and nearby suburbs, Carmel was built with cul-de-sacs on top of old county roads, followed by highways that got widened whenever the population grew. The result: sprawling development and traffic jams.
When Jim investigated the feasibility of roundabouts to reduce traffic congestion, he quickly discovered their safety record. I think it’s easy to picture why a circle would reduce accidents. First, everyone needs to slow down a little to make sure they’re following the curve of the road and taking the correct exit. Second, drivers are more likely to stop looking at their phones or texting because they need to pay attention to the road.
The Insurance Institute for Highway Safety researched the impact of circles on Carmel, which they dubbed “Roundabout City.” They found that the town’s double-teardrop roundabouts—similar to dog bone–shaped roundabouts—reduced injuries from car crashes by 84 percent, and all car crashes were reduced by 63 percent in comparison to rates before the roundabouts’ installation.
Pedestrians and cyclists reap similar benefits because cars slow down and are not crossing intersections to make left turns, Jim says. In many cases, switching to a roundabout instead of adding more motor-vehicle lanes provides an opportunity to add bike lanes, which also increases safety for riders.
Need further proof of the safety benefits? Jim told me that, nationally, 12 out of 100,000 people die because of a traffic fatality. That number is just 2 out of 100,000 in Carmel.
In Oklahoma City and other places, fire departments sometimes worry about whether a roundabout will be wide enough for their vehicles and how they can proceed quickly without the ability to go through red lights. That’s an important piece of the design of each roundabout, because public safety is the ultimate goal. Once first responders recognize the public safety benefits of eliminating T-bone collisions, they realize that roundabouts can be in their best interest, too.
Safety is the most important aspect of any decision leaders make, but what about traffic jams? All this talk about slowing down may make it seem as if people will be stuck longer in their cars, but the truth is that once you eliminate stoplights, traffic keeps flowing. In Carmel, Jim says that 50 percent more cars pass through a roundabout every hour, compared to the number of cars that travel through a regular intersection with traffic signals or stop signs.
You might expect some opposition from residents or retailers once you introduce new street patterns with roundabouts. Some business owners worry that, without a stoplight in front of their store, people might not notice them. But Jim tells me that in Carmel, business owners discovered that they ended up with more business because people realized that they didn’t have to fight traffic to get around town. It’s a nice town to visit, and the locals have come to love their roundabouts. In a recent survey, more than 90 percent of Carmel residents said they approved of roundabouts.
A roundup of case studies about the impact of roundabouts on local economies found positive correlation between this type of traffic improvement and business performance. In Golden, Colorado, there was a 50 percent increase in sales tax revenue and additional retail and office space constructed after a roundabout was installed. In Topeka, Kansas, 92 percent of business owners said their business increased or stayed steady after a roundabout was built nearby. And in Avon, Colorado, sustained sales tax revenue growth occurred in the seven years following a roundabout installation, even during the Great Recession.
Jim believes roundabouts offer a few other benefits, too. Drivers save money on fuel because they aren’t wasting gas while they wait for a lsight to change or for traffic to clear. They burn less fuel when they can keep driving at a steady pace rather than stopping and starting. City engineers in Carmel estimate that drivers in the town save an estimated $14 million annually in gas because of the roundabouts. Auto insurance rates are typically lower in locations with fewer traffic accidents, too, so drivers may save money on those premiums in a town like Carmel, Jim says.
There are environmental benefits, too, because you eliminate emissions from idling cars and the electricity used for stoplights. In Carmel, an estimated 20 tons (18 mt) of carbon emissions are saved per year because of the roundabouts. And, if there’s a power outage, you don’t need to do anything different for driver safety.
Aesthetically, Jim believes roundabouts generate an opportunity for landscaping or public art to be placed in the center of these circles. In Carmel, about 10 percent of the roundabouts have sculptures, and the rest have green space in the median.
Because roads don’t need to be widened to accommodate extra traffic, you can keep plenty of space open for sidewalks, bike lanes, and other uses that encourage walkability.
Cost-benefit analysis
Once people understand the safety benefits of circles and get past the learning curve to drive on a roundabout, the remaining objection typically involves cost. In Oklahoma City, we installed a few roundabouts while I was mayor, and others are planned but awaiting funding.
According to Jim, a stoplight system can cost $500,000 to install and maintain, including $7,000 to $10,000 annually per stoplight. Those lights need to be replaced about every 20 years, and if the power goes out, you may need to pay a police officer to direct traffic. Timing engineers need to be hired to adjust the lights occasionally. If you opt to construct a new road to handle extra traffic, that can cost $12 million to $14 million for a two-lane road. Even widening the road can cost $5 million to $6 million per mile, Jim says.
If you’re building a new road or replacing an intersection with stop signs instead of traffic signals, installing a roundabout instead of a stoplight costs about the same amount of money. If you need to take out a stoplight to add a roundabout, that can require a substantial increase in the budget. In the long run, though, you’ll generate savings if you don’t have to operate and maintain a stoplight.
Jim and I agree: roundabouts can improve any metro area that has suburban sprawl and traffic issues, from Atlanta to Dallas and beyond. Ideally, you would be able to construct a road with a series of roundabouts to stretch out traffic. Although it’s easiest to introduce roundabouts on new roads, a roundabout works as a retrofit in places that lack well-planned street grids to improve the safety of drivers, pedestrians, and bicyclists.
