The new West Line light-rail in Denver includes a 610 ft long basket-handle tied-arch bridge that was moved into position over a major freeway in a single weekend. Courtesy of RTD Denver
Following years of planning, funding, design, and construction, the first section of a highly anticipated extension to Denver’s popular light-rail line will open to riders next week.
April 16, 2013—Since opening in 1994, Denver’s light-rail system has been part of a boom in civic infrastructure projects that has contributed to the city’s vitality and economic health, including new stadiums and museums, a new convention center, and a new airport. The region’s newest light-rail line, the West Rail Line, is the first project to be completed in the monumental FasTracks program, an initiative of the Regional Transportation District (RTD) that will add 122 mi of commuter rail and light-rail and 18 mi of bus rapid transit, including service to Denver International Airport. Another goal of FasTracks is to transform Denver Union Station into a multimodal transit hub.
Funded by a sales tax increase of 0.4 percentage point that was approved by voters in 2004, FasTracks has seen costs mushroom from an original estimate of $4.7 billion to a current projected cost of $7.4 billion. Construction of the 12.1 mi West Rail Line segment began in June 2009 and cost roughly $707 million. Trains will operate at 7.5-minute headways during peak travel, the daily total to be 212 trains. The trip from the Jefferson County Government Center, at the western edge of the metropolitan area, to Denver Union Station, near downtown, will take 41 minutes. Shuttle buses will link the 16th Street Mall to the rest of downtown, and there will also be a new—and free—circulator bus line.
One of the major challenges on the West Rail Line corridor derived from its location. “Our previous projects for the most part have been [on] grade separated, completely exclusive right-of-way, where either we’re sharing that with the highway or the railroad,” says Jim Starling, P.E., M.ASCE, RTD’s project manager for the West Rail Line. “But this project has gone right down through people’s backyards.”
The line was built atop an old, unused railroad corridor that the RTD bought in the 1980s. As the new line comes out of downtown, it passes through an industrial section of the city. After traversing a long linear park for several miles, it enters an area that is primarily residential before running along a state highway.
Homes in the residential area are old, and their utilities weren’t always exactly where the as-built documents said they should be. Some roads had to be closed longer than anticipated. Some backyards, as Starling says, do indeed back up to the alignment; one house actually encroached on the right-of-way, the homeowner having built an addition that went a little too far. “That obviously had to come down,” Starling says.
The West Rail Line will extend for more than 12 mi and include
11 new stations. Courtesy of RTD Denver
While the rest of the system has only five gated grade crossings except at two locations, downtown and Welton Street, where it operates more like a streetcar, this project alone required 20, half of them in residential areas. Mitigating noise was another significant concern for area residents, who wanted less noise not only from the trains but also from the warning bells at the crossing gates. But advocates for the blind pressed for a warning system that would meet the needs of all residents. The solution was to create a warning that could be adjusted to ambient noise. Thus it will be louder during the day, up to a capped amount, and then grow quieter in the evening. The range that planners estimate is between 50 and 70 dB. (The rest of the crossings have bells at the standard level, 90 to 100 dB.)
Completing the project required the construction of 11 new stations, 10 light-rail bridges, 3 street bridge reconstructions, 3 pedestrian bridges, 2 light-rail tunnels, and 1 pedestrian tunnel. The signature bridge of the new line spans busy U.S. 6, which links the center of the city with its western suburbs. To cross it, engineers in the Denver office of David Evans and Associates, Inc., the firm that designed the new line, developed a tied-arch steel bridge of the basket handle type that was built on-site. Typically, such a bridge would be built in two halves, and traffic would be detoured around the half under construction. But in this case the Colorado Department of Transportation didn’t want a center pier for the bridge, so contractors built the entire bridge on-site. Additionally, they were able to move it into place in just one weekend. The RTD says this represents the first time that a bridge of this time has been constructed in this way.
Spanning six lanes and two frontage roads, the bridge extends 610 ft, its main span being 286 ft. It was moved into place with the help two 35 ft transport platforms on the leading edge of the bridge. The trailing edge of the bridge traveled on guided rollers that were pushed by hydraulic rams. The RTD even set up bleachers so that people could observe the move, and there were about 2,000 onlookers.
In all, the bridge contains 600 tons of structural steel and 44 cables that total 1,950 ft in length. The weathered steel will naturally rust to a dark purple-brown color, so the bridge will not need to be repainted over time.
Crews also had to build a 284 ft tunnel to pass beneath Interstate 70 and connect the final leg of the line. They did this by drilling caissons from the abutment walls and building a plate on top of them. “We had utility vaults that would provide access to the caissons, so we could drill it at night,” Starling notes.
To cut costs, the final 3 mi leg of the line, which runs from the Denver Federal Center to the Jefferson County Courthouse, will operate on only a single track. To recover the lost capacity, every other train heading west will travel to the end of the line. What is more, RTD notes that the trains will have three cars rather than two, so capacity shouldn’t be affected. (The platforms through the rest of the system have been upgraded to handle four cars.)
The new line opens April 26; RTD anticipates a daily ridership of 19,300 in the opening year, growing to nearly 30,000 by 2030. John Lackey, P.E., M.ASCE, a vice president in the Denver office of David Evans and Associates, Inc., says plans for a west corridor rail line in Denver date back to the mid-1970s. “It’s been on the books for a very long time. When you add up the number of years between then and now, to see it actually get to opening day is a terrific milestone and a great accomplishment,” he says. “It’s a huge win for the region.”