A total of 748 new cars will be delivered to the Washington metro network in the US by Kawasaki Railcar for $1.48bn.
The Japan-based company will make an initial supply of 364 vehicles, costing $765m, according to railwaygazette.com.
The first 64 cars of the 7000-series will be ordered for Phase 1 of Dulles International Airport Corridor expansion.
Assembled as four semi-permanently coupled cars, the 7000-series will allow running of eight-car trainsets during peak periods.
Delivery of the first 64 cars is expected by 1 April, 2014.
Another 300 units are expected to replace the system's original 35-year-old 1000-series cars.
The delivery of these units are expected to be complete by 1 March, 2016.