Roundabouts: A Safer More Efficient Alternative By Jeff Mehlhaff, SDML Staff When you hear the term, “Roundabout” the first thought that probably comes to mind is the roundabout scene in National Lampoon’s European Vacation or you think of an intersection that looks confusing, complicated and has lots of traffic. While this is a common misperception, roundabouts actually provide a safer, more efficient alternative than traditional intersections. What is a Roundabout? The Federal Highway Administration (FHWA) defines a roundabout as a type of circular intersection with yield control of entering traffic, islands on the approaches and appropriate roadway curvature to reduce vehicle speeds. Why Consider a Roundabout? Compared to other types of intersections, roundabouts have demonstrated safety and other benefits. Roundabouts have been shown to: j Improve Safety x More than 90% reduction in fatalities x 76% reduction in injuries x 35% reduction in all crashes x Slower speeds are generally safer for pedestrians j Reduce Congestion x Efficient during both peak hours and other times x Typically less delay j Reduce pollution and fuel use x Fewer stops, hard accelerations and less time idling
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Save Money x No signal equipment to install, power and maintain x Less right-of-way and pavement required Complements other common community values x Quieter operation x Functional and aesthetically pleasing
The lower left picture indicates the potential vehicle collision points of a traditional intersection and a roundabout. Because of the circular nature of the roundabout head-on and high-speed right angle collisions are practically eliminated. The number of collision points is also greatly reduced with a roundabout. Good Locations for Roundabouts Roundabouts are safe and efficient, but they are not the ideal solution for every intersection. The South Dakota Department of Transportation (SDDOT) looks at several factors when deciding to build a roundabout at an intersection. Engineers consider these characteristics when determining the best solution for a particular intersection: j Crash history x Data about the number of accidents x Type of crashes x Speeds x Other contributing factors j Intersection operation x The level of current and projected travel delay being experienced, and backups on each leg of the intersection. x Types of vehicles using the intersection - This is especially important for intersections frequently used by large trucks. j Cost x Societal cost of crashes x Right-of-way (land purchase) requirements x Long-term maintenance needs Cost and Maintenance of a Roundabout Depending on the situation, there can be little difference in the overall cost and maintenance between a signalized intersection and a roundabout. A roundabout may need more property within the actual intersection, but takes up less space on the streets approaching the roundabout. Roundabouts usually require less overall property to build than a signal with turn lanes because traffic doesn’t have to line up and wait for a green light. Roundabouts eliminate hardware, maintenance and electrical costs associated with traffic signals, which can amount to approximately $5,000 per year. However, there are typically more overhead lights and additional maintenance with the central island
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SOUTH DAKOTA MUNICIPALITIES
