The primary function of the modern roundabout is as an intersection control device, the same basic function provided by a light signal or a stop sign. Modern roundabouts have proven, however, to have many additional benefits far too numerous to ignore and relatively few drawbacks. And yet the modern roundabout is just now gaining popularity in the United States, after being successfully incubated in Europe, Australia and Canada over the past few decades. Even skeptics in transportation planning and engineering fields who seemingly felt the long list of benefits seemed too good to be true have been won over by the wonders of roundabouts. The rising popularity of roundabouts is due to the fact that they reduce traffic delays and crash rates, particularly injury-producing and fatal accidents, as well as reduce construction and maintenance costs, fuel consumption and air pollution.

The Federal Highway Administration (FHWA) officially describes the modern roundabout as "a circular intersection that features channelized approaches, yield control for entry into the circular lanes, and approach geometry that assures vehicle speeds will be less than 30 mph." Traffic can continuously flow through the intersection, giving higher capacity than a similar sized signalized intersection and lower vehicle delays. The fewer potential vehicle conflict points are limited to sideswipes, making any accidents that do occur less severe [see Tab 8].

A 2000 preliminary report by the American Automobile Association Foundation declared, "improved traffic flow, aesthetics, and cost savings make roundabouts a good idea, and the safety gains are compelling."

The state of Maryland has become a leader in the U.S. in installing modern roundabouts, as a logical component of Governor Glendening's smart growth policies and smart transportation planning. The Maryland State Highway Administration feels that "roundabouts can offer a good solution to safety and capacity problems at intersections. At intersections where roundabouts have been installed in Maryland to replace existing intersections, a Maryland study of the first eight roundabouts installed the annual crashes dropped from an average of 5.0 crashes per year before conversion to roundabouts, to 1.8 crashes per year at the roundabouts, a 64% reduction. Crash severity also dropped from an average of 3.0 injury crashes before to 0.5 crashes per year after conversion, an 83% reduction. (Russell, Luttrell, Rys, www.ksu.edu/roundabouts)

Although a listing of current roundabouts on record at "Modern Roundabouts: The Web Site" has no listings for any modern roundabouts in Pennsylvania, PennDOT has anticipated their increasing popularity by publishing the PennDOT Guide to Roundabouts (Publication #414, May 2001 that describes the many benefits of this form of intersection control [see Tab 7]:

A well-designed roundabout has the potential to improve the conditions of an existing intersection or can be a highly effective component of a new transportation system. A modern roundabout offers benefits such as increased safety, increased capacity, reduced delay, and calmer traffic. In addition, air and noise pollution can be reduced and the aesthetics of the area enhanced.