Safety Benefits
The Insurance Institute for Highway Safety publiched a report in March of 2000 entitled Crash Reductions Following Installation of Roundabouts in the United States. The study looked at changes in motor vehicle crashes after the conversion of 24 intersections from stop sign or traffic signal control to roundabouts. It was done in a mix of urban and rural locations, and involved single-lane and two-lane roundabouts.
The study found the following highly significant relationships:
- A reduction in collisions of all types of 40%.
- A reduction in injury collisions of 75%.
- A reduction in fatal and incapacitating collisions of about 90%.
The results are consistent with numerous international studies and suggest that roundabout installation should be strongly promoted as an effective safety treatment for intersections. This is given the large numbers of injury (700,000) and property damage (1,300,000) crashes that occur each year at stop signs and traffic signals in the United States.
Also from the study:
Although the sample was too small to estimate effects on pedestrian crashes, none of the multilane roundabouts have had a single pedestrian crash so far, even though there were two crashes during the before period at these sites. Scandinavian evaluations conclude that single-lane roundabouts are very safe for pedestrians. Data from this study give no reason to doubt that those experiences can be translated to North America. Likewise, Scandinavian experience shows that single-lane roundabouts with one-lane entries are very safe for bicyclists.
Some have expressed concern that older drivers may have difficulties adjusting to roundabouts. However, in this study the average age of crash-involved drivers did not increase following the installation of roundabouts, suggesting that roundabouts do not pose a problem for older drivers.
High Rates of Crashes at Cross Intersections
The cross intersection, the four-leg type of intersection preferred in North America, has been out of favor for many years in other countries because of its high accident rate. Sweden has not used cross intersections in new construction for at least fifteen years. The United Kingdom does not recommend cross intersections in new construction. To reduce collisions, they convert existing cross intersections to offset (jog) intersections and roundabouts. Offset intersections are recommended for light crossing flows and roundabouts for heavy crossing flows.
Cross intersections appear to be the most dangerous type of intersection commonly used in North America. We feel forced to choose the cross intersection to accommodate heavy crossing flows because we do not generally recognize the roundabout as an available intersection choice.
A British text on road layout (Design Bulletin 32, Residential Roads and Footpaths, p. 34. British Department of Transport, 1977) expresses aversion to cross intersections because of their inherent danger: “Cross roads are generally regarded as the most dangerous form of junction, largely because they imply cross traffic movement.... They should therefore normally be avoided.”