Roundabouts have been shown to improve vehicular safety at intersections.

A roundabout is a circular intersection. Traffic maneuvers around the circle in a counterclockwise direction, and then turns right onto the desired street. All traffic yields to vehicles in the roundabout and left-turn movements are eliminated. Unlike a signalized intersection, vehicles generally flow and merge through the roundabout from each approaching street without having to stop.

Roundabouts reduce the number of potential conflict points, compared with traditional intersections. Experience has demonstrated that vehicular crashes are significantly reduced when low-speed, single lane roundabouts replace four-way intersections.

Proper accommodation of pedestrians and bicyclists in roundabouts represents an area of continuing research and development. Properly designed roundabouts include sufficient deflection to ensure low speeds, and splitter islands at the approaches slow vehicles and allow pedestrians to cross one direction of travel at a time. The literature shows that, given a properly designed single-lane roundabout, motorist and pedestrian safety is almost always improved when compared to conventional intersections. Multilane approaches create multiple threats for pedestrians and are not recommended.

The splitter islands at roundabouts allow pedestrians to cross one direction of traffic at a time. This is a significant advantage over conventional intersections. If motorists do not yield to pedestrians at the crosswalk, pedestrians must select a gap in traffic before crossing. If traffic flow is continuous, choosing a gap may become problematic. At multi-lane roundabouts, the nearside vehicle may yield to pedestrians, but traffic in the adjacent lane may not stop, exposing the crossing pedestrians to a potential crash as they proceed through the first lane into the adjacent.

People who are visually impaired must be able to detect where and when to cross, be able to stay in the crossing area, and detect and exit the crossing. Properly designed and installed curb ramps and warning devices at the sidewalk sides of the crossing and in the splitter island aligned with the crosswalks can help address detecting where to cross and exit. The alignment along with highly visible crosswalk markings can assist pedestrians in staying in the crossing. However, detecting when to cross can be a challenge, particularly for multi-lane roundabouts or roundabouts with continuous traffic flow. Studies are being done to consider devices to create a gap in traffic flow or help people with vision impairments select a gap.

Wayfinding and gap selection cues need to be adequately addressed in the design of roundabouts so that roundabouts are not a barrier to pedestrians with vision impairments. Research is currently underway through the National Cooperative Highway Research Program (NCHRP) to further explore the problem and develop potential solutions. Refer to NCHRP Project 3-78, Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities for the latest status report.

Bicyclists may be disadvantaged by some roundabout designs. As with conventional intersections, a cyclist using a roundabout can proceed either as a motor vehicle or as a pedestrian using the sidewalk and marked crosswalks. If proceeding as a motor vehicle, merging with traffic is required at the entry. This may take some skill and judgment but is not unlike traveling though a conventional intersection. Properly designed single lane roundabouts reduce vehicle speeds sufficiently so that most cyclists feel comfortable sharing the road. However, multi-lane roundabout are more difficult for cyclists to traverse due to more complex movements making them less ideal for bicyclists. Marking bicycle lanes through the roundabout has not been shown to be safer. In larger roundabouts, an off-road bicycle path may be necessary to allow cyclists to use the pedestrian route. This is inconvenient and takes longer but it will improve safety. Refer to the FHWA report Roundabouts: An Informational Guide for more information related to the design of facilities for both pedestrians and bicyclists.

Geometric design slows vehicles as they enter the roundabout.


  • Improve safety at intersections, particularly those experiencing a large number of angle collisions
  • Convert signalized intersection to improve traffic flow efficiency
  • Reduce speeds at an intersection
  • Create a gateway into an area


  • Street widths and/or available right-of-way need to be sufficient to accommodate a properly designed roundabout.
  • Roundabouts have a mixed record regarding pedestrian and bicyclist safety—a low design speed is required.
  • Roundabouts are generally not appropriate for the intersection of two multilane roads.
  • Roundabouts often work best where the traffic flows are balanced on all approaches.
  • Deflection on each leg of the intersection must be set to control speeds to 24-29 km/h (15-18 mi/h).

Estimated cost

The cost for a landscaped roundabout varies widely and can range from $45,000 to $150,000 for neighborhood intersections and up to $250,000 for arterial street intersections, not including additional right-of-way acquisition. Yet, roundabouts have lower ongoing maintenance costs than traffic signals.