Dulles rail bridge project looms on horizon at Tysons Corner
Sunday, May 23, 2010
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.