Turbo Roundabouts

Abstract

While concentric two-lane roundabouts have a higher capacity than single-lane roundabouts, they have the disadvantage of a higher driving speed through the roundabout. They also reintroduce the possibility of lane changing on the roundabout and hence raise the risk of accidents. The author developed the turbo roundabout in 1996 in an attempt to deal with these drawbacks. This type of roundabout has the following features: no lane changing on the roundabout, no need to yield to traffic on more than two lanes, and low driving speed through the roundabout because of raised lane dividers. This paper discusses the concept of the turbo roundabout and the details determining success. Studies have shown that the risk of accidents associated with injury is greatly reduced on turbo roundabouts: an 80% reduction has been measured. In view of the known safety trends on single-lane roundabouts, it is recommended that a slightly lower reduction in the accident rate (70%) should be assumed in the long term. Another great advantage of the turbo roundabout is the fact that the traffic flow can be divided over the lanes of the roundabout in a much more balanced way. Since 2000, 70 turbo roundabouts have been built in the Netherlands. The Dutch Information and Technology Platform (CROW) published its guidelines on turbo roundabouts in April 2008.