Cover Story

November/December 2009

Planes and Trains

Sound Transit’s new Airport Link light-rail project offers a vital connection for downtown travelers

By Sheila Bacon Cain

At just 1.7 miles long, the new Airport Link in Seattle may be the shortest segment of Sound Transit’s much longer light-rail project, but it arguably is one of the system’s most complex components.

With overhead and at-grade rail work, construction of a new passenger station and considerable roadway reconstruction to accommodate the route, the $379-million job has kept contractors, the design team and the owner on their toes for the past three years.

Sound Transit’s airport extension, which will open on time in December, is the southernmost piece of a much bigger light-rail project that begins at downtown Seattle’s Westlake Station and extends 15.6 miles south to Sea-Tac International Airport. The initial 13.9-mile segment, which stopped just short of the airport, opened in July.

Traffic Congestion

Traffic coordination arguably was the trickiest aspect of incorporating light-rail track and overhead guideways amid two busy roads serving the airport. Sea-Tac Airport is the nation’s 17th busiest, serving more than 32 million passengers in 2008. During heavy holiday travel, more than 100,000 cars use the northbound and southbound expressways each day. On the port’s slowest days, 60,000 trips are made.

The bulk of the Airport Link rail segment is located on airport property between the two roads. It travels at grade and on an elevated guideway as it makes its way to a new passenger station immediately east of the airport. To accommodate the light rail, each direction of the expressway was widened, requiring extensive detours.

Value engineering scaled back the scope of the pedestrian bridge across International Boulevard, but the new design meant the structure could be brought to the jobsite in several pieces, assembled on-site and lifted into place during the course of just a few hours. (Photo courtesy of Mowat)

Road construction began early in the project and included demolition of a 1.5-mile “return to terminal” loop of roadway north of the existing parking garage, says George England, program leader for the Port of Seattle. Closing this familiar and well-used loop meant cars were temporarily relocated to an upper road. So important was the smooth transition that port authorities implemented an “incident command group” to monitor progress and reroute cars if traffic became too heavy. The three-day job went off “without a hitch,” England says.

The Port of Seattle, which managed the roadwork, and Sound Transit, which oversaw track and station construction, met frequently with a cadre of airport users, including a dozen rental car companies, public and private bus lines, taxi fleets, limousine companies, the airlines and other airport tenants. “We liked to say we communicated with just about everyone in the world,” England says. “Not quite, but it was quite a communications effort.”

While most of the roadwork was completed in August, a final piece of road construction will wrap up next August.

Time to Negotiate

The bulk of the job was placing light rail and constructing a 30,000-sq-ft passenger station, built by Woodinville, Wash.-based Mowat Construction, an AGC of Washington member. A heavy-civil contractor most familiar with public work, Mowat found itself operating in somewhat of a design-build capacity after a too-high bid caused considerable value engineering by its team members.

The Airport Link line travels both at grade and on an elevated guideway system between downtown Seattle and the airport. (Photo courtesy of Mowat)

When the passenger-station contract was let by Sound Transit in March 2007, Mowat was the only bidder, and its bid of $95 million was well above Sound Transit engineers’ $51.8-million estimate. At the time, officials blamed the high bid on the lack of competition and a booming construction environment that kept many potential bidders busy elsewhere.

Sound Transit sought input from its staff, Mowat and the design team to tweak the design and suggest less expensive building methods. Team members compared the engineer’s estimate and the contractor’s bid “line by line,” says Sound Transit project director Ron Lewis, who called the value-engineering sessions “quite illuminating.”

They were quite economical as well. Value engineering shaved $22 million off Mowat’s initial bid, bringing the station contract to $73 million and within reach.

Cutting Back

One of the biggest money-saving efforts was the redesign of the passenger station roof. It originally was designed by Seattle-based Hewitt to be a dramatic structure enveloped in glass, but a number of its structural and design elements were altered. Team members suggested eliminating the glazing, replacing welded structural-steel tubes with less expensive bolted I-beams, replacing tiling material with a polished concrete slab at the mezzanine level and reconfiguring the windscreen. “This was going to be a signature project for light rail,” says Mike Bell, Mowat’s construction manager. “It was neutralized a little.”

The original station roof design called for welded structural-steel tubes and glazing, but both were eliminated, reducing costs considerably. (Photo courtesy of Mowat)

A pedestrian bridge across busy International Boulevard connecting with the station also was redesigned. As drawn, it was to be a built-in-place steel-frame structure with a design that echoed the original station. Money-saving efforts included narrowing the structure and building it off-site.

Value-engineering efforts on behalf of the Chehalis, Wash., office of rail subcontractor RailWorks also helped tighten the budget, Bell says. The at-grade portion of the light-rail track originally was designed as direct fixation track, which included a concrete slab with rail-supporting curbs, or plinths. Designing the section instead as ballasted track with crushed-rock subgrade supporting ties and rail was simpler and offered a savings of $1 million, Bell says.

Continuing Down the Line

A 2⁄3-mi portion of elevated guideway work was performed by Bellevue, Wash.-based PCL Construction, an AGC of Washington member and one of Sound Transit’s contractors for six miles of earlier light-rail work. The elevated work was a change order to its original contract. PCL’s work begins at the completed passenger station in Tukwila and continues south to the beginning of Mowat’s work at South 160th Street in SeaTac.

This section of guideway was designed and constructed as precast segmental concrete, a method PCL used on its original contract. “[This] allowed for the construction of the substructure to occur simultaneously with the fabrication of the precast superstructure,” says Chris Stack, PCL’s senior project manager. “Construction of the elevated guideway by any other means and methods would not have allowed us to complete the work within the same time frame as our original contract.”

PCL’s initial contract included the use of a massive overhead erection gantry used to lift and place the concrete segments. For the additional work, however, crews used conventional cranes and falsework.

Long-Range Vision

The completion of the Airport Link project fulfills Sound Transit’s long-standing vision to offer light-rail service between downtown Seattle and the airport. An extension of the light rail north from downtown Seattle to the University of Washington—a 3.15-mile segment—is under way and scheduled to open in 2016. In 2008, voters approved 36 miles of north, east and south extensions, with completion expected between 2020 and 2023.

As the first of any light-rail work in the region, Sound Transit’s segment from downtown Seattle to the airport is important infrastructure that will give commuters another transportation option.

The Airport Link in particular is a key project, especially when the construction industry is in a recession, says Jerry Dinndorf, AGC of Washington’s Seattle district manager. “Sound Transit’s projects are one of the few bright spots for construction in this down economy,” Dinndorf says. “The Airport Link and U-Link work—the last two projects in Sound Transit’s phase- one program—are big-dollar efforts that are providing needed work for a variety of contractors, from demolition to heavy- highway/civil and building contractors.”