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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 2019, PennDOT released data for 19 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 19 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 2018 shows:

  • Fatalities were reduced by 100 percent (from two to zero);
  • Serious injuries were reduced by 90 percent (from 10 to one);
  • Minor injuries were reduced by 79 percent (from 24 to five);
  • Possible/unknown severity injuries were reduced by 81 percent (from 70 to 13);
  • Crashes causing only property damage increased by 10 percent (from 69 to 76); and
  • The total number of crashes dropped 34 percent (from 138 to 91).
In addition to the 19 roundabouts meeting the review criteria, 29 other roundabouts have been installed on state routes and over 40 are in design. 

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)