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Roundabouts

Safety Aspects

Roundabouts offer improved safety over other at-grade intersection forms primarily because roundabouts have fewer conflict points, slower speeds, and easier decision making.

Roundabouts are geometrically designed to reduce vehicle speeds to generally 25 mph or less, and all turns are right turns. This significantly reduces the severity of crashes over those at traditional intersections. Crashes that do occur are typically low-speed, sideswipe crashes rather than high-speed T-bone collisions that can occur at traditional intersections especially with left-turn movements.

Roundabouts also improve pedestrian safety due to the slow speeds and by providing a media refuse area. This allows for two simple crossings of one-way traffic.

Safety Statistics

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.

In September 2020, PennDOT released data for 22 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 22 comprise all the roundabouts on state routes that met the review parameters. Department data based on police-submitted crash reports spanning the years 2000 through 2019 shows:

  • Fatalities were reduced by 100 percent;
  • Suspected serious injuries were reduced by 77 percent;
  • Suspected minor injuries were reduced by 57 percent;
  • Possible/unknown severity injuries were reduced by 82 percent;
  • Crashes causing only property damage increased by 21 percent; and
  • The total number of crashes dropped 21 percent.

In addition to the 22 roundabouts meeting the review criteria, over 30 other roundabouts have been installed on state routes and over 40 more are in design.

Capacity

Roundabouts typically carry about 30 percent more vehicles than similarly sized signalized intersections during peak traffic conditions. During off-peak conditions, roundabouts cause almost no delay, unlike traffic signals which can cause delay to side street and traffic turning left from the major street. The increased capacity and efficiency of roundabouts is due to the generally continuous slow-flowing nature of entering vehicles yielding to circulating vehicles rather than waiting for a signal to turn green. It should be emphasized that entering vehicles are required to yield to pedestrians and the circulating traffic, which commonly requires stopping, especially during peak traffic conditions.

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. The primary keys for motorists to navigating a roundabout are to slow down, yield to pedestrians, and yield to the circulating traffic.

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)