Kawasaki Heavy Industries Ltd. said Friday it has been unofficially awarded an order worth about $880 million to deliver 428 subway cars to the Washington Metropolitan Area Transit Authority.

The contract will include an option provision in which the Washington metro authority may place an order for up to an additional 320 cars, making it possible for KHI to receive its biggest-ever single train order, worth a total of about $1.48 billion if the option is exercised, the company said.

Kawasaki Heavy plans to assemble and test the 428 cars at its plant in Nebraska, and deliver them from 2013 to 2016, it said, adding that the firm would continue the production until 2018 if it receives the additional order, it said.

The new cars will be introduced in line with the Washington metro authority's plan to extend its subway networks as well as to replace its old cars. Kawasaki Heavy said it has earlier received orders for more than 3,000 train cars combined in the United States from the New York City Transit and other customers.