Metro tests out their new 7000 series subway cars on May, 20, 2014 in Shady Grove, Md. (Bill O'Leary/The Washington Post)

After years of design work and months of testing, Metro plans to debut its newest generation of rail cars April 14 on the Blue Line, introducing a subway train unlike any other in the four-decade history of the transit system.

Eight of the cars, called the 7000 series, or 7Ks, will leave Metro’s Franconia-Springfield station that Tuesday morning as one train, the agency announced Thursday. Eight more 7K cars, already delivered to Metro by the Kawasaki Rail Car Co. in Nebraska, will begin service as a second train a few weeks after the first, officials said.

Interim General Manager Jack Requa said Metro is ready to tell Kawasaki to start production of 512 more 7Ks for which funding was approved long ago. And government officials in the District, Maryland and Virginia said this month that their jurisdictions will pay for an additional 220 7Ks, for a total of 748 new cars by the end of the decade, costing about $2 billion.

“It’s been a very long time,” Requa told reporters after making the announcement at a meeting of Metro’s board of directors. “We’ve talked about it for years. We’ve been testing it for a long time. We believe it’s ready to go. We know it’s ready to go.”

Since the mid-1970s, when the Washington area’s subway system opened, Metro has purchased more than 1,100 cars in six batches. Nearly all are still on the rails. Because the agency wanted each new batch to be mechanically compatible with previous ones, officials said, Metro did not take full advantage of improvements in technology.

Metro tests new 7000 series subway cars on May, 20, 2014 in Shady Grove, Md. (Bill O'Leary/The Washington Post)

The new, advanced-technology cars are a radical departure from the past. The 7Ks are so different from the cars in Metro’s current fleet that they cannot be coupled with the older cars and will run as separate, eight-car trains, the agency said.

With frames of stainless steel rather than aluminum, the new cars include seating layouts and digital passenger-information systems that Metro said are more rider-friendly. The cars would hold up better in a collision, according to the agency. And the blue color scheme of the interior is more modern than the disco-era earth tones to which area subway riders are accustomed.

The main impetus for the 7K plan was the 2009 Red Line crash near the Fort Totten station that killed eight passengers and a train operator.

All the victims were aboard 1000-series cars, the oldest in Metro’s fleet. The National Transportation Safety Board later determined that the 300 cars of the 1000 series, built in the 1970s, were structurally outmoded and not “crashworthy.” In an urgent safety recommendation, the NTSB called for Metro to scrap the 1000 series.

For almost six years, however, the 1000-series cars have remained in service as Metro went through the long process of choosing a contractor for the new series, then oversaw the design, testing and manufacturing of the 7Ks.

And at least in the near future, the 1000-series cars will continue carrying passengers, according to Metro. The 16 new 7Ks that have been delivered and the first 48 cars due to arrive in coming months will be used for fleet expansion, to meet demand created by last summer’s opening of the Silver Line, Metro said.

Only when more 7Ks arrive, perhaps next year, will the transit agency begin retiring the 1000-series cars. “I would not commit to a date” for scrapping the old cars “until I get a production schedule from Kawasaki, and what their capabilities are,” said Deputy General Manager Rob Troup, Metro’s No. 2 official.

“Obviously, it’s an NTSB recommendation,” he said of getting rid of the 1000-series cars. “We want to get those cars off. We want to be able to do it.”

The first train of 7K cars will debut on the Blue Line (but will be exclusive to the Blue Line for only a limited period) in an apparent goodwill gesture by Metro toward riders on the Virginia end of that line, who have been inconvenienced in recent months.

In a change in the frequency of train service resulting the opening of the Silver Line in July, rush-hour Blue Line passengers south of Rosslyn have been forced to wait longer for trains (12 minutes) than they had in the past, which has generated many complaints. So Metro said it will allow those riders to be the first to experience the 7Ks.

“It’s dedicated to the Blue Line for the initial few days — the initial days of service,” Requa said.

When Requa was asked when the first new 7K train would begin to be used on other subway lines, Metro spokesman Dan Stessel leaned in and answered for him. “It’s assigned to the Blue Line,” Stessel said. But for how long? “It’s assigned to the Blue Line,” he repeated. “That’s the answer.”

After retiring the 1000-series cars and also scrapping the 100 trouble-plagued cars of the 4000 series (built in the early 1990s), Metro’s long-term grand plan is to use the 748 new cars to beef up morning and evening rush-hour service. During those peak periods, the agency hopes to run only eight-car trains, eliminating six-car trains.

However, that will require more than $850 million in electrical power upgrades and infrastructure improvements in the subway, Metro has said. Although Maryland, Virginia and the District have agreed to finance the purchase of the new cars, transportation officials in those jurisdictions aren’t ready to give the agency an additonal $850 million.

An array of problems with maintenance and emergency preparedness in the Metro system were revealed by a Jan. 12 incident near the L’Enfant Plaza station in which an electrical malfunction filled a subway tunnel with noxious fumes, sickening scores of passengers on a train. A 61-year-old Alexandria woman died of smoke inhalation.

And in recent weeks, a raft of financial problems have come to light in the agency.

Until Metro demonstrates that those issues have been corrected, the region’s transportation leaders have said, money for the all-eight-car-train plan will not be forthcoming.

“In my opinion, I believe that discussions of expansion have to be deferred for maintenance,” Maryland Transportation Secretary Peter K. Rahn said in an interview this week. “And it means saying no to some popular things until [Metro] has addressed throughout its system the issues of performance and safety.”

Rahn said: “This is a three-jurisdiction issue — four, if you count the feds — and we can’t dictate how it’s going to go. But we are certainly going to express our opinion.”

Abigail Hauslohner and Robert McCartney contributed to this report.