A standard four-way intersection has 32 potential collision points when all the turning movements from each of the roadway approaches are counted; roundabouts have only eight potential conflict points.
The center island of a roundabout also eliminates the possibility of head-on collisions. The English/Frost intersection will generally have 1.0 million vehicles entering every 45 days. The intersection had four to eight accidents each year and two were classified as serious.
Maplewood city officials anticipate that accidents at this intersection could be reduced by 33 percent with the addition of the roundabout and none of these collisions should be serious.
The curving nature of the roundabout approaches and the inner circular island require travel speeds to be low to maneuver through the intersection.
According to guidelines established by the Federal Highway Administration, speed in a roundabout on a minor roadway, such as the intersection of Frost Avenue and English Street in Maplewood, is restricted to 15 mph. This slower speed also requires smaller gaps in the circulating traffic for vehicles trying to enter the roundabout.
A typical intersection signal system costs $200,000 and takes 2-3 years of study, planning and fabrication time before it can be installed. The cost of the roundabout at English Street and Frost Avenue was about $150,000 to install. In addition, the roundabout does not require electricity to operate.
Roundabouts also create much less delay and pollution than other traffic control devices, have a higher vehicle capacity, and require very little maintenance.