A view from the center to the end of the new rail car shows the new floor, rails and seats. (Robert Thomson – The Washington Post)

Metro formally unveiled its subway cars of the future Monday — four shiny, stainless-steel conveyances representing the most significant changes in engineering and industrial design in the transit system’s 37-year history.

The four new cars — the first of 748 due to be delivered by 2018, at a cost of about $2 billion — are a technological and aesthetic break with the past for Metro. From the mid-1970s through 2008, the agency acquired six batches of subway cars (1,134 cars in all), most of which continue in use. Each batch was designed to be compatible with the others, mechanically and stylistically, so that they they could be grouped together in trains.

The new cars of the 7000 series, however, will run as separate trains, apart from the older cars.

At a ceremony attended by an array of elected officials — Maryland Gov. Martin O’Malley; Maryland’s two U.S. senators, Barbara Mikulski and Ben Cardin; D.C. Mayor Vincent Gray and others — the four cars rolled out of a rail yard and into the nearby Greenbelt Metro station, where the officials were given a tour. The cars, built in Lincoln, Neb., will be tested on Metro’s track for several months before being put into service.

With a blue interior color scheme, improved safety features, more standing room, digital information displays and enhanced audio systems, the cars are a radical departure from the brushed-aluminum, earth-toned, less technologically advanced subway cars that Washington-area commuters have long been accustomed to.

The 748 cars will constitute half of Metro’s rail fleet by the time the last one arrives in 2018 and nearly 400 0lder cars have been retired, the agency said.