The Benefits of Going ‘Round in Circles

Wednesday, December 1, 2021

A recent New York Times Article titled These Americans Are Just Going Around in Circles. It Helps the Climate. discusses the positive impacts that Roundabouts have had in Carmel, Indiana. Carmel is just north of Indianapolis and has 140 roundabouts, more than any other city in the United States. For decades, traffic engineers have cited the improved crash safety of roundabouts versus other intersections.

Residents of Carmel list many other benefits of these intersections. For example, Carmel found that roundabouts alleviated rush hour backlogs and stops. Roundabouts don’t require electricity to control traffic, which is a major boon during the more frequent storms the US has seen in recent years. When storms knock out power and back up traffic in signaled intersections, roundabout intersections still flow smoothly. Well-designed roundabouts are also more friendly to cyclists and pedestrians than signaled intersections.

But Carmel also sees positive environmental impacts. Since roundabouts don’t require cars to stop and idle at red lights, gasoline consumption is reduced. As stated in the article, the Federal Highway Administration has said that the reduction in emissions compared to signalized intersections can be significant. Specific to Carmel, the former city engineer believes the city’s roundabouts have resulted in a reduction of 20,000 gallons of gas used per year. And the city has landscaped its roundabouts, delivering more green space than signaled intersections that handle an equivalent amount of traffic.

MS2’s team has also studied roundabouts for many years. Our Transportation Data Management System (TDMS) is used by numerous agencies to measure the changes in crashes at intersections before and after the construction of roundabouts in their jurisdictions. Our TDMS clearly shows how well their roundabouts are performing. The data yielded by our TDMS can also be paired with US government economic data to calculate the financial impact of roundabouts.

In 2020, MS2 published a comprehensive report that measured the actual crash experiences at modern roundabout intersections, including the economic cost of these crashes. Our report evaluates the before-after crash experiences at twelve intersections in Washtenaw County where modern roundabouts replaced existing intersections. In this study, MS2 used our TDMS to identify traffic crash characteristics at each intersection prior to roundabout construction, then compared those characteristics with post-construction statistics. By comparing the crash characteristics with the economic crash cost before and after roundabout construction, MS2 identified the net benefit/detriment achieved through implementing roundabouts. For most roundabouts, our findings echo the experience of the city of Carmel. Other roundabouts, however, are a totally different story. Read our Roundabouts report to learn how to measure the results of the roundabouts in your jurisdiction.