Do roundabouts work for bicycles and pedestrians?
Modern roundabouts by their design require motorists to slow down typically to less than 25 mph (40 km/h), and preferably 15 mph (25 km/h) to proceed through the intersection. The literature shows that, given a properly designed single-lane roundabout, motorist and pedestrian safety is almost always improved when compared to conventional intersections. Results regarding cyclist safety are somewhat mixed. Roundabouts have fewer conflict points and lower speeds compared to conventional intersections, resulting in a significant overall reduction in the severity of crashes for all users, although the frequency of some crashes may increase. Multi-lane roundabouts present some challenges to pedestrians, thus reducing the safety effects that roundabouts provide.
A bicyclist navigates a roundabout on a bridge in Olympia, Washington. Ramps allow bicyclists to act as pedestrians as well as vehicles.
Photo: Dan Burden, from www.pedbikeimages.org.
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. Motorists must detect cyclists upon entry, circulating and exiting so as not to merge into or turn in front of them. As with complex intersections with multiple turn lanes, a multi-lane roundabout also becomes more difficult for cyclists to traverse.
Splitter islands allow pedestrians to cross one direction of traffic at a time.
Photo: www.pedbikeimages.org.
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.
In summary, single-lane roundabouts, in particular, can work well for most cyclists and pedestrians if properly designed and implemented. Lower operating speeds compared to conventional intersections reduce the overall severity of crashes that do occur. Multi-lane roundabouts that would be found on multi-lane roadways are not going to make these corridors work better for cyclists or pedestrians, but their lower operating speeds have some advantage. More work is required to ensure that people who are visually impaired can be well-accommodated at roundabouts.
Additional resources:
http://www.tac-atc.ca/english/resourcecentre/readingroom/conference/conf2004/docs/s20/Furtado.pdf
http://www.tfhrc.gov/safety/pedbike/pubs/05080/
http://www.tfhrc.gov/safety/00068.htm
http://www.walkinginfo.org/engineering/roadway-roundabouts.cfm
http://www.trb.org/TRBNet/ProjectDisplay.asp?ProjectID=834
