By Lisa Rein
Washington Post Staff Writer
Sunday, May 23, 2010; C01
Drivers who have already suffered through a year of road and rail construction in Northern Virginia will soon have a dazzling new distraction: a flyover that will carry Metrorail trains 30 feet above the Capital Beltway on their way toward Dulles International Airport.
At its highest point, the bridge will rise 65 feet above Tysons Corner, the heart of the new Silver Line. It will begin its ascent along the Dulles Connector Road north of Interstate 66, cross to the north side of Route 123, then swoop over the Beltway before the trains dive under Route 7. Workers will begin this week to assemble the first segments.
It will be an engineering marvel to some but an eyesore to others -- those who fought for three years for a tunnel to carry the trains under Tysons.
The construction technique to be used over the Beltway is a high-wire engineering act, in which hundreds of 10-by-17-foot, 25-ton blocks of concrete will be suspended from a massive metal overhead crane, a yellow submarine on stilts extending over 12 traffic lanes.
The Beltway bridge, known as an aerial guideway, will also rise over workers building ramps, abutments and roadbeds for the Beltway, which is expanding to accommodate 14 miles of high-occupancy toll lanes.
In addition, crews at Tysons are raising the Beltway three feet. Below them, ironworkers and pile drivers are at work on Route 123, the spine of Tysons, building piers to support the HOT lanes.
"We're obviously in their back yard, and they're in our back yard," said Shawn MacCormack, aerial structures chief for Dulles Transit Partners, the contractor building the first 11.7 miles of the 23-mile rail line. "Building is the easy part. Working in such a heavily populated area, in and around live traffic, is the real challenge."
The construction at the juncture of two of the country's biggest road and rail projects is so potentially dangerous that most of the work must be done in daylight, MacCormack said. Traffic will be stop-and-go as the guideway marches above it, making the gridlock of the past year seem like a cakewalk. The construction will create some of the longest delays of the three-year megaprojects.
"There will be a lot more going on, and things will be crazier," said Jamie Breme, a spokeswoman for the $1.9 billion HOT lanes project. "It's the most complex part of both projects. Motorists are going to see an impact."Lego on steroids
Many motorists have noticed the yellow behemoth that took up residence this month in the median of the Connector Road.
It's an overhead crane called a truss, custom-built to hoist each of the rail line's elevated segments into place between the giant piers along the line's path and to propel itself by remote control from one stretch to the next. The truss weighs 366 tons and stretches about 360 feet, but it takes up less space than the multiple ground-based cranes and trucks used to build standard girder or beam bridges with 100-foot-long decks.
The truss has raised eyebrows in Hallcrest Heights, a townhouse community in McLean directly behind the Connector Road. From Gary Deger's house, it looks like Lego blocks on steroids.
"I've never seen anything like it," the chemical engineer said, eyeing the truss one morning last week. "The first time I saw it, I thought, 'That's just not normal.' "
By the time the first leg of the rail line, from East Falls Church to Wiehle Avenue in Reston, is finished, in 2013, the truss will have assembled 2,763 segments to carry inbound and outbound trains. But the Beltway bridge will be the most visible.
At $170 million, the six miles of elevated track will be the costliest and most intricate feature of the $5.2 billion Silver Line. But the track will cost at least $200 million less than a four-mile tunnel under Tysons pushed by many residents, local officials and developers when Virginia sought federal funding for the project. Sending the trains underground could have sunk the rail line, so the tunnel became a casualty, although crews are digging a half-mile tube under Route 123 that will connect two of the Metro stations in Tysons.
Some backers of a longer tunnel are still seething.
"At the end of the day, it's an elevated train that's urban-looking and noisy," said Pamela Konde, president of the Greater Tysons Green Civic Association, which represents 350 homes off Old Courthouse Road. She calls the Beltway bridge a "roller coaster."
"It was political expediency," Konde said.
Bill Szymanski, who lives on Tysons' Vienna side, said he regrets that tunnel supporters did not circulate an image of the guideway during the debate. "It's going to open people's eyes what they're building over those piers," he said. "It will be a huge visual distraction. Rather than unifying Tysons, it's going to divide it."Higher and higher
The flyover has been more than two years in the making, from its design to the foundations that workers have hammered in under the roads this year. The team of 200 workers is led by MacCormack, a quiet, 39-year-old Canadian in flannel shirt and jeans whose office is a construction trailer. His childhood on rural Prince Edward Island hardly prepared him for building urban bridges. But he has risen to the top of a small fraternity of engineers trained in the sequential assembly of bridges in small pieces, a technique used increasingly in urban areas to minimize traffic disruption.
He's passionate about the job, moving his young family from job to job, building segmental bridges in Massachusetts, Maine and Tacoma, Wash. The challenge is huge -- fitting together a 2,763-piece jigsaw puzzle as the truss lifts each custom-made segment of elevated track bed.
The concrete is poured into molds in a remote area at Dulles Airport. The segments come out looking identical, but each one is different, destined for a particular spot in a particular span. Each segment arrives by truck, and the truss lifts it in place, where it is joined with epoxy to the segment next to it. Then steel cables called tendons are threaded through the segments to bind them together. In the final alignment, all the pieces are locked in place, and the truss is ready to move on.
Engineers then use a remote control to activate motors on both sides of the truss. It will take about seven minutes to advance to the next pier, anywhere from 120 to 150 feet away.
The track will go higher and higher until its peak at the Beltway, where an army of ironworkers, crane operators, laborers, carpenters and pile drivers will continue the process. Under them, other crews will be replacing the northbound Beltway bridge over Route 123 with a six-lane span.
MacCormack called the guideway job the biggest logistical challenge of his career.
"It's going to be awesome," he said. "It's going to smack you in the face by the time summer gets here."