The final span for the bridges that will carry the Dulles Corridor Metrorail Project’s Silver Line trains through Tysons Corner was lowered into place this Tuesday in the median of the Dulles International Airport Access Highway/Dulles Toll Road corridor.

The span was put in place using a 365-ton horizontal crane, also known as a truss. The final span included 12 segments, each weighing between 25 and 40 tons. “This is a major construction milestone for Phase 1 of the project, which will connect Tysons Corner and Reston to Metro’s existing Orange line and the entire 106 mile metrorail system,” said Patrick Nowakowsi, Executive Director of the rail project, which is being built by the Metropolitan Washington Airports Authority. “We plan to complete construction this time next summer and Metro will open Phase 1 in the late 2013.” During construction of the aerial guideway structure in Tysons, three large trusses, also known as launching gantries, were used to move the massive concrete and steel segments into place.

Approximately 2,700 segments were used to create the 3-mile stretch. Each segment was custom-made on the grounds of Dulles Airport and transported individually by truck to Tysons Corner. With the completion of the final span, the truss will be dismantled. Crews will now begin laying track, building cable troughs and performing additional systems work.