Data analysis shows major safety benefits for roundabouts in Pennsylvania


The Pennsylvania Department of Transportation (PennDOT) has announced that according to a review of its latest departmental data, crashes, injuries, and fatalities have markedly decreased at 11 roundabouts after they were installed.

PennDOT recently reviewed data for 11 roundabouts at intersections on state routes that were previously stop-sin or traffic signal controlled. These roundabouts were reviewed based on having at least three years of data available before and after the roundabout’s installation, and 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% (from two to zero);

• Serious injuries were reduced by 100% (from seven to zero);

• Minor injuries were reduced by 95% (from 19 to one);

• Possible/unknown severity injuries were reduced by 92% (from 49 to four);

• Crashes causing only property damage decreased by 2% (from 49 to 48);

• The total number of crashes overall dropped by 47% (from 101 to 54).

In addition to the 11 roundabouts meeting the review criteria, 32 other roundabouts have been installed on state routes and 26 are in design.

Widely used in the UK and across mainland Europe, roundabouts are gaining traction across the USA, where they are often known as traffic circles, rotaries or gyratories. Roundabouts are frequently installed to address intersections with safety issues, but may also be installed to improve traffic flow, as well as other reasons such as traffic calming and to facilitate pedestrian mobility. Although roundabouts are safer and typically more efficient than traditional signalized intersections, in many cases they may not be the best option due to topography or other reasons, such as property impacts, capacity issues and proximity to other intersections.

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

Roundabouts typically carry about 30% 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 pre-timed signal. To help increase safety further by educating Pennsylvanians on how to navigate a roundabout, PennDOT has created a video that shows the public how to use both single and multi-lane roundabouts, whether in a vehicle, on a bicycle or on foot.

“Our data shows that modern-day roundabouts reduce crash severity and injuries while improving traffic flow,” said PennDOT secretary Leslie S Richards. “This underscores why roundabouts are becoming more commonplace in Pennsylvania and beyond.” 

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Adam joined the company in 1994, and has been News Editor of TTT since 2009. In his other role as Circulation Manager, he helped create the original Traffic Technology International distribution list 23 years ago, and has been working on it ever since. Outside of work, he is a keen fisherman, runs a drumming band, and plays an ancient version of cricket.