You might be wrong about roundabouts

Misconceptions about roundabouts - circular intersections that are cropping up all over Georgia  -- abound with regard to everything from how they work, to how safe they are, to what they cost.

Georgia Department of Transportation has a good instructional video on roundabouts. And with the help of Scott E. Zehngraff, assistant state traffic engineer, we can now dispel some of the myths about them.

August 19, 2015 - A roundabout under construction at the intersection with Northridge Road and Somerset Court in Sandy Springs. BOB ANDRES / BANDRES@AJC.COM

Myth #1: Roundabouts can't handle as much traffic as an intersection with a traffic signal: The roundabout can handle potentially more traffic than a typical intersection, depending on the site. If two roads feeding into the intersection have the same amount of traffic or a 70/30 split, the roundabout will operate better. However, if the main road carries 90 percent of the traffic and a side street carries 10 percent of the traffic, a traffic signal is probably a better option than a roundabout. That's because you can program a traffic signal to prioritize the main route. Also, a dense urban area that has signals spaced closely together is probably better served by a traffic signal.

Myth #2: It costs more to build a roundabout than to install a traffic signal. At locations that don’t already have left or right turn lanes, a roundabout could be cheaper to install than a traffic signal. That's because when a traffic signal is installed, left and right turn lanes usually need to be added for the intersection to function well. Roundabouts are also less costly because there's no technology to install or maintain. In addition, the sometimes smaller footprint of a roundabout means the state doesn’t need to buy as much land. For example, a roundabout in Covington at the intersection of Ga. 81 and Ga. 162 was projected to cost between $511,000 and $744,000 to build. Installing a stop-and-go traffic signal would have cost $868,000.

Myth #3 Roundabouts are less safe for motorists than intersections with traffic lights. According to Zehngraff, "a roundabout is proven to be significantly safer." A big reason for that is that they force motorists to slow down as they approach and they eliminate cross-traffic turns. Statistically, intersections with roundabouts have a:

  • 78% reduction in injury crashes over signalized intersections
  • 82% reduction in injury crashes over two-way stop controlled intersections.
  • 75% reduction in conflict points over a traditional four-way intersection.
  • 100% reduction in crossing conflict points over a traditional four-way intersection.

Myth #4 Roundabouts are more dangerous for bicyclists and pedestrians. Actually, the opposite is true. In a traditional intersection, cars are driving through at 40 or 50 mph. At a roundabout, they are having to slow down to 20 mph, which reduces the severity of car-versus-bicyclist accidents. A roundabout also greatly reduces the number of potential conflict points between a driver and bicyclist who is traveling in the middle of the roadway as a vehicle would, from 32 at a traditional signalized intersection to just 8. For pedestrians, reduced vehicle speeds are also a lifesaver. Additionally, at a roundabout pedestrians only cross one direction of vehicular traffic at a time. A median or a splitter island always separates the opposing directions of traffic.

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