Maryland Pushes New 'Diverging-Diamond' Interchange Design For Road Junction

WASHINGTON -- Just one day after local planning activists panned a proposed "diverging diamond" interchange near the Greenbelt Metrorail station in Prince George's County, the Maryland Department of Transportation's State Highway Administration and the Cordish Companies announced Tuesday that a busy interchange in neighboring Anne Arundel County would be reconfigured in a similar fashion.

According to a media advisory, the diverging-diamond interchange planned for the junction of Arundel Mills Boulevard and Maryland's Highway 295 is "an innovative, award-winning traffic solution that has worked successfully around the country to improve traffic flow and efficiency."

With diverging-diamond interchanges, traffic going either direction on an overpass crosses paths twice at signaled intersections. The design allows for traffic entering an onramp or exiting an offramp to easily merge into traffic, eliminating the need for turn lanes and long traffic signal cycles.

From the media advisory:

"The innovative Diverging Diamond interchange at MD 295 and Arundel Mills Boulevard will be the first in Maryland, so there may be a learning curve for motorists during their initial drive through it," said State Highway District Engineer Lee Starkloff. "We appreciate drivers' patience during construction and urge extra caution through the work zone. When complete, along with the other area improvements, the new interchange will serve long-term transportation needs and improve mobility through the region."

While such interchanges may be designed to better accomodate cars passing through, Greater Greater Washington on Monday dismissed a proposal for redesigning the intersection of Greenbelt Road and Maryland Highway 193 with a diverging diamond as being unfriendly and dangerous for pedestrians and bicyclists:

None of the planners, and especially not the traffic engineer leading this part of the discussion, saw any conflict between turning one section of Greenbelt Road into a micro-freeway while turning the next block into a pedestrian-friendly urban district.

At least it's not as crazy as the so-called "Magic Roundabout" in Swindon, England. Trying to build one of those locally would likely cause heads to spin.

Image from Wikimedia