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Roundabouts

Safety

Roundabouts offer improved safety over other at-grade intersection forms because roundabouts have fewer conflict points, slower speeds, and easier decision making. When comparing a roundabout to a signal, studies show that roundabouts provide a 90 percent reduction in fatal crashes, 75 percent reduction in injury crashes, 30-40 percent reduction in pedestrian crashes, and 10 percent reduction in bicycle crashes. Roundabouts improve pedestrian safety offering two simple crossings of one-way traffic moving at much slower speeds.

In September 2018, PennDOT released data for 11 roundabouts on state routes at intersections that were previously stop or signal controlled. These roundabouts were reviewed based on having at least three years of data available before and after the roundabout's installation. These 11 are all the roundabouts on state routes that met the review parameters. Department data based on police-submitted crash reports spanning the years 2000 through 2017 shows:

  • Fatalities were reduced by 100 percent (from two to zero);
  • Serious injuries were reduced by 100 percent (from seven to zero);
  • Minor injuries were reduced by 95 percent (from 19 to one);
  • Possible/unknown severity injuries were reduced by 92 percent (from 49 to four);
  • Crashes causing only property damage decreased by 2 percent (from 49 to 48); and
  • The total number of crashes dropped 47 percent (from 101 to 54).

Capacity

Roundabouts typically carry about 30 percent more vehicles than similarly sized signalized intersections during peak flow conditions. During off-peak conditions, roundabouts cause almost no delay, but traffic signals can cause delay to side street and left-turning traffic from the major street. Increased capacity at roundabouts is due to the continuously flowing nature of yielding only until a gap is available, versus waiting turns at a signal.

Videos

Because Pennsylvania is on track to install more roundabouts in the coming years, we've created this video to show you just how easy they are to navigate. After you watch the video, you'll know how to use both single and multi-lane roundabouts whether in a vehicle, on a bicycle or on foot. Keys to navigating a roundabout are to slow down and yield.

Swarthmore Borough in Delaware County constructed a roundabout on Chester Road (SR 0320). The video below gives an overview of the development and execution of the roundabout project to create a safer route for drivers and pedestrians. (Courtesy of McMahon Associates)