Connecticut DOT earns national recognition for roundabout conversion

By Chris McCahill

Rotaries—or large, high-speed traffic circles—are common in Northeastern states and are scattered throughout the U.S. In light of their poor performance and safety record, however, some transportation agencies are ditching rotaries in favor of smaller modern roundabouts. In 2008, the Connecticut DOT chose several sites to test these conversions. At the close of 2013, FHWA awarded one of those projects for its success in lowering traffic speeds and reducing crashes and injuries.

Rotaries were originally intended to allow fluid traffic flow through busy, at-grade intersections. While this concept has proven successful in modern roundabouts (a distinctly different type of intersection), the high-speed nature of rotaries makes them considerably less safe and prone to failure on high-volume routes. The Massachusetts DOT chose to replace one high-volume rotary with a flyover interchange, with mixed results. Elsewhere, such as in New York, DOTs are opting for the smaller, less expensive roundabout solution. At one more drastic conversion in Kingston, NY, the DOT successfully replaced a 660-foot diameter rotary with a roundabout one-third its size.

Connecticut’s award-winning roundabout conversion in the town of Killingworth (pictured below) is decidedly less grand, but the results are remarkable. ConnDOT decreased the pavement widths and increased horizontal deflection on an existing traffic circle by adding splitter islands on the approaches and a mountable truck apron around the central island (key features of modern roundabouts).

rotary-roundabout

Travel speeds through the new roundabout are now 15 to 20 mph for all movements, minimizing speed differentials and virtually eliminating the risk of serious crashes. Comparing data from several years before and after the change, the agency found that crashes were reduced by 50% and injuries were reduced by 83%. ConnDOT, along with many other DOTs, have since installed roundabouts at many problematic intersections. While the projects sometimes are met with public opposition, particularly in places where the intersection type is unfamiliar, the outcomes are generally positive. FHWA provides more information on modern roundabouts at its safety program website.

Chris McCahill is a Senior Associate at SSTI.