Bicycle Safety Guide and Countermeasure Selection System
Example of a bicyclist sharing the lane through a single-lane roundabout http://www.pedbikeimages.org/ - Carl Sundstrom
A modern roundabout is built with a large, usually circular, raised island located at the intersection of two or more streets and may take the place of a signalized intersection. Traffic maneuvers around the circle in a counterclockwise direction, and then turns right onto the desired street. Entering traffic yields to traffic 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. If properly designed, roundabouts force slow intersection speeds and reduce the number of conflict areas.
Roundabouts need to accommodate bicyclists and pedestrians. A properly designed roundabout (through widths and deflection) will have operating speeds that are slow enough for a bicyclist to navigate the roundabout comfortably in mixed traffic. Thus, at roundabout approaches with bike lanes, the bike lane will end and the bicyclist will merge into traffic to navigate through the roundabout. Alternatively, for bicyclists uncomfortable at roundabouts, a bicycle ramp may be provided to the sidewalk such that they may dismount and continue through the intersection using the crosswalks as a pedestrian. However, such ramps may be confused with pedestrian ramps and should be reserved for locations where the higher speeds or traffic volumes may result in uncomfortable conditions for bicyclists. Bike lanes are not recommended in the circulatory roadway of the roundabout.
The interest in mini-roundabouts (single-lane roundabouts with an inscribed diameter between 50 to 90 ft) is also on the rise. This type of roundabout provides the safety and operational benefits of a roundabout with a smaller footprint and lower cost and can be a good solution on lower volume roadways.
Multilane roundabouts tend to have higher motor vehicle speeds due to their location on multilane roads and create more conflicts between bicycles (and pedestrians) and motor vehicles. Given these higher speeds and volumes, they can present a challenge to bicyclists and may not make the corridor safer for their use.
Roundabouts are circular intersections designed to eliminate left turns by requiring traffic to exit to the right of the circle. Roundabouts are installed to reduce vehicular speeds; improve safety at intersections through eliminating angle collisions; help traffic flow more efficiently and reduce operational costs when converting from signalized intersections; and help create gateway treatments to signify the entrance of a special district or area.
For neighborhood intersections a roundabout can be installed for approximately $25,000 to $100,000, with landscaped roundabouts raising the cost from $45,000 to $150,000. For arterial streets the cost is approximately $250,000, but can be more than $500,000 depending on the size, site conditions, and whether right-of-way acquisitions are needed. Two-lane roundabouts cost approximately $330,000. Roundabouts usually have lower ongoing maintenance costs than traffic signals, depending on whether the roundabout is landscaped.
Authors and Acknowledgements