The interior of the Orange Line mockup car at the T's Wellington yard in Medford.

A HOLDUP IN THE TESTING of a new vehicle signal system will delay the introduction of new Orange Line cars by at least eight to 10 weeks, MBTA officials said on Monday.

The MBTA had hoped to begin introducing the new vehicles into passenger service this month, but Jeffrey Gonneville, the T’s deputy general manager, said a vehicle signal system developed by a subcontractor on the project needs to be fully checked out by an independent third party and that process will not be completed until mid-March. He said the vehicles should enter passenger service about two weeks after the testing work is completed.

Gonneville said T officials had hoped the test would be done by now. He stressed that no issue has been found with the vehicles themselves and the testing of the vehicle signal system will not delay production, manufacturing, delivery, or acceptance of the cars. He said all of the new vehicles are on track to be delivered by 2022.

“This is probably the last critical item that we have to get resolved,” Gonneville said. ‘We want to get these new cars in service, but we want to do it right.”

The vehicle signal system was developed by a French contractor named Alstom. The signal system operates somewhat like an air traffic controller for subway trains, allowing the transit agency to bunch the trains closer together by overseeing how fast they go, when they brake, and how far apart they operate from each other. The system is considered a key part of the T’s effort to significantly decrease the amount of time, or headways, between trains at stations.

Launching the system is complicated by the fact that initially the new vehicles will operate using the T’s existing signal system but must also be capable of switching over to a largely new signal system once that system is in place. As part of the effort to introduce the new Orange Line vehicles into the system, Gonneville said he plans to intersperse them — empty, without passengers — in existing train sets over the next month or so. The approach will allow T officials to see how the new vehicles operate up and down the Orange Line.

Bruce Mohl oversees the production of content and edits reports, along with carrying out his own reporting with a particular focus on transportation, energy, and climate issues. He previously worked...