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Thursday, May 13, 2010

Dulles Metrorail building bridges for rails in Tysons Corner, Va.

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Construction will begin soon on what can best be described as "bridges" over Tysons. One will begin in May on the Dulles Connector Road (Route 267) and cross over Route 123 to the northwest side of southbound Route 123. Another will cross I-495. Another will be built in the median of Route 7 from just west of Route 123 and into the median of the Dulles Airport Access Highway and the Dulles Toll Road.

These bridges are really guideways, or aerial foundations, to carry the tracks for the Dulles Corridor Metrorail Project.

Construction of the new rail line, an extension of existing Metrorail service from East Falls Church to Dulles Airport and eastern Loudoun County, is being built in two phases. Phase 1 work is well under way from I-66 to Wiehle Avenue in Reston. Four stations will serve Tysons Corner.

The first of those 366-ton trusses is now visible near the Dulles Connector Road and Route 123 where construction of piers that will support the aerial guideways have been built in recent months. Soon it will be used to build the spans of the aerial guideway between those piers. In a few months, other trusses will be assembled to erect guideways that cross I-495 and in the middle of Route 7.

Segments are manufactured off-site at a precast facility near Dulles Airport.

Of the entire Phase 1 alignment of 11.7 miles, three miles of inbound and outbound guideway will be aerial - or a total of six miles of aerial track. The average aboveground height is 35.7 feet.

Aerial guideway begins where the new line splits off from the existing WMATA Orange Line tracks just before the West Falls Church Metrorail Station and yard. It will fly over the westbound lanes of I-66 and descend to the median of the Dulles Connector Road (Route 267). 

Aerial guideway resumes at the Connector Road near the Chain Bridge Road overpass, then crosses over the eastbound lanes of the Connector Road onto the northwest side of Route 123, and into the Tysons East Station. The rail will continue at elevated level, flying over I-495 and into the Tysons Central 123 Station where the rail line briefly goes underground. 

The tunnel portion resurfaces in the median of Route 7, at the Tysons Central 7 Station. From there, the rail line goes aerial again along the median of Route 7 to the Dulles Toll Road. One more flyover takes the guideway westward from Route 7, and the guideway then begins its descent to the median of the Dulles International Airport Access Highway, reaching ground level well before Wolf Trap National Park for the Performing Arts.

The guideway will be constructed by connecting more than 2,700 concrete segments, each weighing about 25 to 40 tons, using massive pieces of equipment called trusses.

Rizzani de Eccher, headquartered in Italy, is the subcontractor that is fabricating the precast segments. The aerial team consists of leadership from Dulles Transit Partners (design/build contractor) and Rizzani's U.S. division. This team brings a combined experience of 50-plus years working on worldwide aerial and bridge projects.

Construction of caissons, piers and pier caps to support the aerial guideway has been under way for several months and is very visible in the median of the Dulles Connector Road. The superstructure will begin at the Tysons East guideway, at the Dulles Connector Road and Route 123 and move across I-495. Expected completion: Late 2011.

Cost of the aerial guideway construction is $170 million.