A railroad runs through it: Design considerations for car-train roundabouts

In a Sunday letter to the editor, "Roundabout might be a better solution than new Stadium Boulevard bridges", Howard P. Fox of Scio Township suggests that a modern roundabout might be a suitable and less expensive traffic control system than replacing the aging bridges that currently carry Stadium Boulevard over State Street and the Ann Arbor Railroad tracks.

Although roundabouts are often considered when intersections are redesigned, the unusual configuration of this particular intersection would seem to argue against a roundabout: after all, there is an active railroad line right in the middle of it. A little research shows that though unusual, this configuration is not completely impossible — and, indeed, it has been already anticipated by the investigative reporting team of the Ann Arbor Newshawks.

No, no, and no

The City of Ann Arbor engineering department has already rejected the idea of a grade level crossing at Stadium Boulevard. In a letter of September 17, 2007 to University of Michigan planner Susan J. D. Gott, city engineer Michael G. Nearing spelled out the impact of putting in a busy signalized intersection at State and Stadium. With more than 45,000 vehicles per day through that corner, traffic models predict 19 new crashes per year. The letter does not analyze a roundabout as a traffic control device and presumes that the intersection will have traffic signals.

The design of a roundabout at this intersection would need to cope with an active railroad crossing running right through the middle of it. Needless to say this is not an ordinary circumstance, but it has been contemplated. In Roundabouts: An informational guide, the US Department of Transportation spells out guidance, which is clear: "A new intersection should not be designed with railroad tracks passing through the center of it." Nevertheless, highway designers recognize that rail lines do pass through existing intersections, and the guide shows some ways of controlling access to keep traffic from backing up onto the tracks.

Courtesy FHWA

Planning in Wisconsin, building in Connecticut

Highway engineers in Wisconsin working on new roundabouts for SR-35 put together a technical report, Traffic Control Considerations for Roundabouts Built Near Rail Lines, in 2007. In it, they note that a number of construction projects which would call for roundabouts are inevitably going to be near active rail lines, and they discuss the best practices and municipal experiences with proposed and built roundabouts.

In Stafford, Connecticut, the Stafford Springs Roundabout at Hay Market Square dates to 1894. The roundabout was modernized in 2006, and is located adjacent to a rail line.

Heavy rail roundabout in Florida

The most unusual roundabout I located is in Jensen Beach, Florida, the only one that I have located to date which has a busy railroad freight line running smack through the middle of it. Designed by Michael Wallwork of Alternate Street Design, it accommodates over 29,000 cars per day and acts as a gateway to the city's Main Street.

Jensen Beach, Florida Railroad Roundabout by Michael Wallwork, www.roundabouts.net

Ann Arbor Newshawks weigh in

The Ann Arbor Newshawks produce a funny quarterly investigative video report on issues of interest to Ann Arbor. They addressed the question of car-train roundabouts a full year ago in their winter 2010 report; jump to 5:24 for their insightful analysis of bridge alternatives.