The Washington Metropolitan Area Transit Authority unveiled a new full-scale mock-up of its next generation railcar, the 7000 series, at an event in 2012. (Mark Gail/For The Washington Post)

The debut of Metro’s long-awaited next generation of rail cars may be delayed, after the independent committee that monitors Metro said the transit agency has been moving too fast in evaluating the cars’ safety, officials said Thursday.

Inching toward their debut for years, the 7000 series cars feature advanced technology and a rider-friendly design far different from what Metrorail customers are used to. The first batch of eight cars — out of 748 Metro hopes to eventually acquire — are scheduled to begin carrying passengers in early January.

But the Tri-State Oversight Committee, which monitors Metro’s compliance with safety rules, could put a crimp in that schedule. TOC Chairman Klara Baryshev said Thursday that Metro engineers have not been thorough in verifying that the eight cars meet all safety requirements specified by the designers.

“There is a list of hazards in the beginning that need to be engineered out, if possible, or they have to be mitigated — and to be sure it’s done, you have to verify,” Baryshev said in an interview after addressing members of Metro’s board of directors.

“But [Metro] does it randomly,” she said. “They take one item, they verify it in car number one, for example. They take another item, verify it in car number two. The problem is, they do not verify every item in every car. It’s random verification.”

James Ojio, of Koshii Maxelum America Inc., photographs ceiling panels made by his company inside of Metro's new 7000 series railcar full-scale mock-up unveiled in 2012 in Landover. (Mark Gail/For The Washington Post)

Although TOC has no enforcement power over Metro, it is unlikely that the transit agency would begin carrying passengers in the new cars without the approval of the watchdog committee, whose members are from the District, Maryland and Virginia.

Testing on the eight cars started early this year, and Metro officials recently said they were confident that the cars would go into “revenue service” at the start of 2015. General Manager Richard Sarles said he looked forward to joining other paying customers using a 7000 series car before he retires in January.

“Now I’m less certain of that,” Sarles said Thursday after Baryshev addressed the Metro board’s safety and security committee. Baryshev spoke about the problem in relatively general terms. The Metro committee then asked her to explain TOC’s concerns in a detailed letter to the transit agency within a week.

“We’ve been testing this set of cars for eight or nine months now, and we’ve been very thorough in what we’re doing,” Sarles said. But he said he would not discuss TOC’s specific concerns until he receives the letter. “We’re really looking forward to hearing the details from them, and when we do, we’ll address them.”

Asked whether the cars’ debut could be delayed if Metro has to conduct a more comprehensive safety evaluation, he said: “There is that potential. I hope that doesn’t occur, because from what I understand from our engineers . . . this has been very, very thorough testing. But until I hear the specifics [from TOC], I don’t know.”

The oversight group and Metro have had strained relations. At times, for example, TOC has been denied access to some Metro records. But officials of the transit agency and the watchdog committee have said they are trying to improve the relationship.

“We work with [Metro] from Day One on safety certification,” Baryshev said. “But now we have our concerns on how the process is being followed.”

Metro has a contract with Kawasaki Rail Car, in Lincoln, Neb., to purchase 528 of the new cars, including the eight that are being tested.

The transit agency has asked the Washington-area jurisdictions it serves to appropriate $1.4 billion so it can buy an additional 220 cars and make related infrastructure improvements to the rail system.