Buses can follow trains along portions of the alignment of the new Green Line through the University of Minnesota. Photograph by Robb Williamson/AECOM
Engineers tweak the alignment of new rail line between Minneapolis and St. Paul to avoid a stadium and encourage transit-oriented development.
June 17, 2014—A $957-million, nearly 11 mi long light-rail line between Minneapolis and St. Paul—which will double the size of the Twin Cities’ light-rail network—opened on June 14, just in time for baseball’s All-Star Game in Minneapolis in July. Trains were expected to make the trip between the two downtowns in about 40 minutes.
The Green Line is the second line in the Twin Cities’ slowly growing light-rail system. The first, the Blue Line, opened in 2004 and travels 12.3 mi between downtown Minneapolis and the Mall of America, connecting with Minneapolis-St. Paul International Airport along the way. The new line has more than 9.8 mi of new track, along with an additional 1 mi of track it will share with the Blue Line in Minneapolis.
Engineers faced their share of challenges bringing the project to fruition. The first was the Washington Avenue Bridge, which links the University of Minnesota’s West Bank campus (near downtown Minneapolis) with its East Bank campus and is capped by a pedestrian deck. According to Chuck Hymes, P.E., M.ASCE, a vice president of AECOM and the company’s project manager, the conceptual design of the light-rail project envisioned some level of rehabilitation on the bridge, but when the nearby Interstate 35W bridge collapsed in 2007, AECOM took a closer look at the Washington Avenue Bridge. Hymes and his colleagues realized it was a fracture-critical bridge. (The Federal Highway Administration defines a bridge with a fracture critical member as one having “a steel member in tension, or with a tension element, whose failure would probably cause a portion of or the entire bridge to collapse.”)
So the engineers converted the bridge to a redundant structure by adding two lines of truss members to each side of the bridge, and then installing a composite deck. This turned, he says, “two two-girder bridges into a single eight-girder and truss bridge.” Engineers also removed chloride that had built up on the piers to extend the life of the concrete, and strengthened the piers to take the loads from the new truss members.
The alignment called for the Green Line to cross the Mississippi over the bridge, travel through the university, pass through a tunnel, and then continue on to downtown St. Paul. But as those plans were coming together, the university revealed plans for a new football stadium, right within the footprint of the tunnel alignment, according to Jim Alexander, P.E., the design manager for the project for Metro Transit, the Twin Cities transit agency.
Alexander developed two alignments to solve the problem—one maintained the tunnel but relocated it, the other put the line at grade—and found, not surprisingly, that the at-grade alignment was significantly less expensive.
While building underground would have allowed automobile traffic to continue on Washington Avenue, which slices the east campus in half, university officials wanted to close the road to automobile traffic anyway. And the underground option would have required a more complicated subterranean station.
The alignment across the university will feature a lane for bikes and emergency vehicles. A short segment of the line will even allow buses onto the guideway—directly in front of or behind the trains. This is not a common approach, but Alexander says it has been done elsewhere, including in Calgary. Signage and enforcement will be critical to prevent cars from following buses into the guideway. “We’re going to see how that goes,” Alexander says.
The last tweak to the conceptual design happened at the other end of the line, in St. Paul: engineers ran the rail line diagonally through a downtown block, which sped up the train’s alignment and reduced the need for a station. It is also expected to lure transit-oriented development to that site.
Given the addition of the Green Line and the capacity that it adds to the Blue Line, Metro Transit required a more robust operations and maintenance facility. Engineers found an abandoned building downtown just beyond the line’s terminus at Union Depot.
The job also required the complete reconstruction of 6 mi of University Avenue, a busy thoroughfare between the campus and St. Paul. Utilities were relocated from the median to the outside of the streets or the sidewalks, and lighting and traffic signals were replaced. A storm-water collection system was revamped as well.
Coordination is key to a job like this, which crosses so many jurisdictions. “It isn’t like you’re building a stadium,” says Alexander. “You’re going from downtown Minneapolis to downtown St. Paul. And there are so many different entities you need to contend with.” There are more than 1,400 businesses, plus community stakeholders and a variety of government agencies—including a watershed district, a capitol area, two counties, and, of course, two cities. Alexander says that only 90 businesses closed and 27 more relocated during the construction.
Learned lessons from the Blue Line informed the designs of the Green Line stations. “A lot of [the Blue Line] stations had their own look about them,” says Alexander. “Canopies looked a lot different from one station to another. Even some of the layouts were a little different.” For the new line, Alexander says the agency wanted more consistency. For one thing, that should make maintenance easier—for example, right now if a piece of glass on a Blue Line station is broken, repair crews have many sizes of glass available in storage. A unified design will simplify storage and repairs.
Additionally, the stations are taking advantage of public art. “The public art is very important for the city and the community, to try to get that neighborhood feel [in] each of the stations,” says Alexander. “We hired artists to work on each of the stations.” The architects and artists collaborated to integrate art into each station from the start. “Art is not just an element to be plopped down,” he says.
Metro Transit estimates that by 2030 the Green Line will serve more than 40,000 passengers per day. The agency is already planning a 16 mi extension to the Green Line, which will operate from downtown Minneapolis to the southwest suburbs. The 16-station project is projected to cost around $1.7 billion. Construction could begin as early as 2016.