All metro trains operating in the U.S. capital may be replaced by ones made by Japanese firms if the operator procures additional rolling stock from Hitachi Ltd., the Washington Metropolitan Area Transit Authority has said.

Since Kawasaki Heavy Industries Ltd.'s 7000-series already accounts for over half of the rolling stock in the city, all the metro cars will be supplied by Japanese makers if the authority fully exercises its contract with Hitachi Rail Washington LLC to procure up to 800 rail cars.

Hitachi Rail Washington won a contract in March to design and manufacture 256 cars of the 8000-series with an option to build up to 800 cars, in a deal worth up to $2.2 billion, for the metro service.

The new 8000-series railcars, designed to be lighter and more energy-efficient, will be built at a new Hitachi factory in the U.S. capital and are slated to be put into operation in 2025.

A WMATA official said the authority plans to replace all the aging vehicles made by a European maker and provide a unified metro service with Japanese trains if it decides to go ahead with the maximum order of 800 rail cars from Hitachi.

Problems with the old trains have plagued the Washington Metro. The replacements may allow the Japanese firms to showcase their products to global markets if they can earn a good reputation in the city.

As for Hitachi train cars, taking thorough safety measures will be one of the company's most urgent priorities after cracks were discovered in some parts of the Hitachi Class 800 series operating in Britain, causing disruptions to high-speed rail services there in early May.

The WMATA operates six metro lines serving 91 stations in the Washington metropolitan area.