It was the final journey Thursday morning for dozens of Orange Line train cars that were retired from service by the MBTA, some after more than 40 years of riding the tracks that stretch from Forest Hills neighborhood of Jamaica Plain to Oak Grove in Malden.

The cars, some in service since the Nixon administration in the 1970s, are being replaced by “more modern, more efficient and more spacious vehicles,” as part of the MBTA $9.6 billion investment in the overhaul of the T service.

Most commuters on the Orange Line Monday morning rode in comfort in the new cars; the agency introduced 60 cars into service configured into 10 trains.

The introduction en masse of the new cars coincided with the reopening of the service after the unprecedented 30-day shuttering of the line that allowed the agency to work around the clock to address safety problems and complete a laundry list of construction projects.

More:MBTA Green, Orange lines up and running after 30-day stoppage, commuters were delighted

Commuters had already glimpsed the new cars earlier in the spring; however the MBTA pulled them from service after several glitches were discovered, including an issue with a battery and improperly installed brake bolts on seven of the cars.

As part of its safety overhaul, the MBTA reconfigured the protocol for acceptance of vehicles as they are delivered to the agency by CRRC MA Corp., a Chinese company building the cars in Springfield.

MBTA General Manager Steve Poftak has said the new procedure can pinpoint and intercept issues before the cars are deployed. But even with the new protocols, issues can still crop up; one of the new cars experienced a door malfunction Tuesday and the entire train was removed from service, according to the MBTA. Passengers boarded the next train.

It was a minor issue, according to the MBTA, isolated to one door on an entire six-car train and it was returned to service Wednesday morning.

The retirees were trucked to Middleboro where the Costello Dismantling Company will turn them into scrap.

The agency has also ordered 100 new trolley cars, Type 10 “Super Cars,” for the Green Line from CAF USA Inc., an $810 million contract to design and construct the trolleys. Currently in the design phase, the new cars could be rolling on the expanded Green Line by 2026.

“This is an incredible moment that marks an inflection point for the MBTA Green Line riders as we continue to work to transform the entire line,” Poftak said earlier in September. “Not only will the Type 10 “supercars” provide more capacity (they are 40 feet longer than existing cars), and a roomier ride for what is the nation’s busiest light rail line, but they also include the latest safety technology, accessibility improvements (wider doors), and other upgrades that improve the rider experience.”

A portion of the Green Line, from Government Center to the Union Square spur, was also shuttered for the same 30-day period as the Orange Line, as construction work to complete the extension through Medford continued. Those five stations — three new stations in Somerville and two in Medford — are expected to be open to riders by the end of 2022.

Portions of the D-Branch of the Green Line will close intermittently throughout the fall starting Sept. 24 as the MBTA addresses track issues and the installation of the Green Line Train Protection System. There will be three nine-day closures through the end of October.

Other branches of the Green Line were closed through the summer, including B, C and E branches with the E-branch closed for 16 days for track replacement and installation of the protection system.

Demolition work at the Government Center Garage in June also prompted the MBTA to temporarily shutter service on both the Orange and Green lines to protect the safety of workers and riders as the structure was being demolished.

It was a trying summer for the MBTA and its customers.

The Federal Transit Administration spent months reviewing the agency and its operations after finding a “higher overall rate of reportable safety events” when compared to other transit systems nationwide.

The incidents and accidents included a July train fire that forced the evacuation of some 200 riders onto a bridge over the Mystic River on the Orange Line, runaway train cars in different car yards and a door malfunction that caused a dragging death, among others.

The resulting FTA safety report, issued Aug. 31, pinpointed several issues that contributed to the deficiencies in the MBTA. These included a finding that the state Department of Public Utilities (DPU) failed to adequately oversee the agency and also failed to flex its regulatory muscle to ensure problems identified in a 2019 report were addressed. That 2019 report was an earlier look at the system by an independent Safety Panel convened by the MBTA’s Fiscal Management and Control Board.

The agency viewed many of the incidents and accidents on the MBTA as one-off or freak occurrences rather than the systemic failure of the entire system.

In its August report, the FTA also cited massive cuts of “hundreds of millions of dollars” from its operating and maintenance budgets from 2015 through 2019. Those cuts dominoed into a lack of enough personnel to effectively run the agency, over-reliance on overtime, and overworked and undertrained personnel.

The FTA also highlighted the agency’s decision to prioritize delivering on its capital projects over passenger operations, preventative maintenance and even safety.

According to the report, the agency has a deficit of nearly 800 employees, from engineers to dispatchers, car maintenance crews to drivers. Signs in MBTA vehicles indicate that the agency is hiring and invite riders to apply for positions ranging from hands-on jobs to office positions and everything in between.

Investment in the MBTA has increased recently, however, with the state legislators voting $600 million to the agency before the end of its session in July.