Capital Rail Constructors, a joint venture of Clark Construction Group and Kiewit Infrastructure South with Parsons acting lead designer will be responsible for the $US 1.2bn Package A, which covers around half of the construction work required for the $US 2.7bn project.

A contract for project management services has also been awarded to Jacobs Engineering, continuing the role it performed on Phase 1.

The 18.3km six-station extension is due to be completed in 2018, when it will be handed over to Washington Metropolitan Area Transit Authority.

MWAA says the initial $US 2.9bn phase of the Silver Line from Church Falls to Wiehle Avenue is now 90% complete and on schedule to open later this year.