The basket tied-handle arch bridge carrying the West Corridor light rail will cross over the Sixth Avenue Freeway right above the path of a former freight rail spur that until 1988 crossed the freeway at grade with a signalized crossing. Courtesy RTD.

By Kevin Flynn
Inside-Lane.com

“Roll Out the Barrel” is a polka standard, but Roll Out the Light Rail Bridge is anything but standard in construction.

Late next month, the weekend of April 23-26, metro residents will get to see a first-of-its-kind construction method in the United States.

The signature steel-arch bridge for RTD’s West Corridor light rail over the Sixth Avenue Freeway will be rolled into place, literally, over the highway from its temporary perch on a platform at the Denver Federal Center. This innovative construction method promises to save time and money for the traveling public and taxpayers.

The bridge is called a basket tied-handle arch; it resembles the curved handle of a wicker basket with the two sides angling in toward each other and meeting or “tied” at the top of the arch.

This temporary platform on the Denver Federal Center serves as a stage to build the arch; it will be launched over Sixth Avenue in April to connect with the pier at right rear, on the north side. Courtesy RTD.

The late Dennis Cole, who was RTD’s project manager for the West Corridor construction, once described it as “like the Egyptians built the pyramids.”

The installation will require a full closure of Sixth Avenue between Kipling Street and Simms-Union for the weekend of April 23-26. The Colorado Department of Transportation, RTD, West Corridor contractor Denver Transit Construction Group and bridge-building subcontractor Edward Kraemer & Sons collaborated to get the installation ready for a weekend after the height of ski season travel and before the start of the heavy summer driving season, to minimize the impact on traffic.

But the unusual method of installation also minimizes the need for recurring lane closures that would have been required under more standard construction methods with workers out in the middle of and over the freeway for months.

The bridge superstructure has been going up piece by piece on the south side of the freeway on the Denver Federal Center. The U.S. General Services Administration, which operates the center, and Lakewood officials worked closely with RTD to get the transit agency to adopt this signature bridge style.

RTD's initial design for the bridge was a traditional Warren truss-type span. Lakewood and the GSA lobbied for the arch style. Courtesy RTD.

But the city and the GSA, with plans to develop the federal center into a mixed-use commercial area, wanted something more memorable than that. Together they ran estimates showing that the basket tied-handle arch would be less expensive. RTD was persuaded and the swap was done.

“The entire steel arch structure is fabricated from weathering steel and the arches incline inwards toward each other to form a ‘basket-handled tied arch’ style of bridge,” RTD says in its latest West Corridor newsletter. “The tensioned cables are 2 3/8” inch diameter galvanized steel and are arranged in a crossed-cable pattern that provide an important piece of the structural integrity as well as being visually attractive.”

After it is connected to the side span already in place over the north frontage road, Kraemer’s crews will begin installing the concrete decking.

RTD photo shows Kraemer's construction reaching the apex of the arch.