Roundabouts are circular intersections in which all vehicles travel in a counter-clockwise direction. Compared with signalized and stop controlled intersections, roundabouts are safer, lower maintenance, more efficient, better for the environment and more aesthetically pleasing.

Fun Facts

Safety — Roundabouts have been shown to reduce fatal and injury crashes as much as 75 percent! The reduction in crashes is attributed to slower speeds and reduced number of conflict points.

Low maintenance — Roundabouts eliminate maintenance and electricity costs associated with traffic signals. This can mean as savings of as much as $5,000 a year per intersection.

Capacity — By yielding at the entry rather than stopping and waiting for a green light, the delay is significantly reduced.

Environment — Fewer delays and less engine idling translate to decreased fuel consumption and cleaner air.

Aesthetics — The central island provides an opportunity to beautify the intersection with landscaping.

How do roundabouts affect traffic flow?

Certainly a number of studies conducted by the Traffic Institute and others have reported significant improvements in traffic flow following conversion of traditional intersections to roundabouts.

A recent study documented missed opportunities to improve traffic flow and safety at 10 urban intersections suitable for roundabouts where either traffic signals were installed or major modifications were made to signalized intersections. It was estimated that the use of roundabouts instead of traffic signals at these 10 intersections would have reduced vehicle delays by 62-74 percent. This is equivalent to approximately 325,000 fewer hours of vehicle delay on an annual basis.

Or, for a more entertaining way of learning how roundabouts affect traffic flow, take a look at what Jamie Hyneman and Adam Savage, from Discovery Channel’s “Mythbusters” found: http://www.youtube.com/watch?v=OvoFjirrgYA.

Can roundabouts accommodate larger vehicles?

Yes. To accommodate vehicles with large turning radii such as trucks, buses, and tractor-trailers, roundabouts provide an area between the circulatory roadway and the central island, known as a truck apron, over which the rear wheels of these vehicles can safely track. The truck apron generally is composed of a different colored material than the paved surface, usually a reddish colored concrete, to discourage routine use by smaller vehicles.

Are roundabouts safe for pedestrians?

Roundabouts generally are safer for pedestrians than traditional intersections. In a roundabout, pedestrians walk on sidewalks around the perimeter of the circulatory roadway. If it is necessary for pedestrians to cross the roadway, they cross only one direction of traffic at a time. In addition, crossing distances are relatively short, and traffic speeds are lower than at traditional intersections. Studies in Europe indicate that, on average, converting conventional intersections to roundabouts can reduce pedestrian crashes by about 75 percent. Single-lane roundabouts, in particular, have been reported to involve substantially lower pedestrian crash rates than comparable intersections with traffic signals.

Do roundabouts require more space than traditional intersections?

Roundabouts do not necessarily require more space than traditional intersections. Geometric design details vary from site to site and must take into account traffic volumes, land use, topography, and other factors. Because they can process traffic more efficiently than traffic signals and stop signs, roundabouts typically require fewer traffic lanes to accommodate the same amount of traffic.

In some cases, roundabouts can require more space than stop signs or traffic signals at the actual intersection to accommodate the central island and circulating lanes, but approaches to roundabouts typically require fewer traffic lanes and less right-of-way than those at traditional intersections.

Are there other benefits?

Because roundabouts improve the efficiency of traffic flow, they also reduce vehicle emissions and fuel consumption. In one study, replacing a signalized intersection with a roundabout reduced carbon monoxide emissions by 29 percent and nitrous oxide emissions by 21 percent. In another study, replacing traffic signals and stop signs with roundabouts reduced carbon monoxide emissions by 32 percent, nitrous oxide emissions by 34 percent, carbon dioxide emissions by 37 percent, and hydrocarbon emissions by 42 percent. Constructing roundabouts in place of traffic signals can reduce fuel consumption by about 30 percent. At 10 intersections studied in Virginia, this amounted to more than 200,000 gallons of fuel per year. And roundabouts can enhance aesthetics by providing landscaping opportunities.

Ariana Green is the Transportation Agency for Monterey County’s Complete Streets Coordinator. If you have any questions, you can reach her at (831) 775-4403, or via email at: ariana@tamcmonterey.org