BOSTON – With more new train cars on the tracks and the elimination of six “slow zones,” the MBTA declared its 30-day Orange Line shutdown “successful” and reopened service to passengers at 5:16 a.m. Monday with trains departing from Oak Grove and Forest Hills stations.

The T also reopened the Green Line Extension service between Union Square and Government Center after a partial shutdown on that line that officials said was required to accomplish work to get ready to open the Medford branch of the extension in late November. Work conducted during the shutdown will enable the T to lift a “slow zone” over the East Cambridge Viaduct, MBTA General Manager Steve Poftak said at a press conference on Sunday.

“I truly believe we are turning a corner with this Orange Line surge,” Poftak said.

With critical upgrades in place, now it’s up to the T, where safety woes have drawn federal intervention, to deliver on “safe, accessible, smooth and convenient” public transit, as Transportation Secretary Jamey Tesler put it. The Orange Line provides about 101,000 trips each day or about half of its pre-pandemic volume.

The T will continue to use “surges” and “diversions” – government terminology for shutdowns that divert riders and enable quicker construction timetables, though at a smaller scale. The T plans temporary shutdowns, Poftak said, with limited shutdowns coming soon on the Green Line’s D branch and early closures planned on the Red Line’s Braintree branch to give crews bigger windows to perform overnight work.

The MBTA, which was reporting delays on Green and Line routes Monday due to mechanical and signal problems, also tweeted Monday morning that it was handing out $5 gift cards to Dunkin’ at select stations “as a small thank you for our riders’ patience during the 30-day diversion.”

Gov. Charlie Baker joined Poftak and Tesler at the Tufts Medical Center station Sunday and said the T had been able in 30 days to complete five years’ worth of track and signal infrastructure upgrades while addressing “safety actions on a much faster timeline.”

Baker said 72 new Orange Line cars would be “ready to go” Monday, up from 30 new cars before the shutdown.

As of 10:30 a.m. Monday, TransitMatters, a transit advocacy group in Boston that offers live tracking of subway service – reported all 10 trains operating on the Orange Line this morning were new car models.

Federal intervention and directives spurred the T and the Baker administration to take on the compressed work schedule, which Baker called “the longest service diversion overseen by the T for an entire line.”

Crews replaced about 14,000 feet of rail and more than 2,000 railroad ties during the shutdowns, Baker said, contrasting that with about 35,000 feet of rail replacement along the Green Line over the past five years.

The MBTA maintenance team fixed the slow zone between Downtown Crossing and State Street, which had been identified as one of the highest priority repairs, in two days during the diversion, Poftak said. Normally, these repairs would have taken the team 39 days of overnight and weekend work.

“We think [divergence] is an important tool, I think the FTA’s special directive on track maintenance has reinforced that for us,” he said. “These diversions are a great way for us to get aggressive after some track maintenance issues.”

Over the next month, the MBTA will use three nine-day diversions on areas of the Green Line’s D Line to make repairs.

Though Orange Line service has returned, some changes to the commuter rail that helped alleviate commuters’ burdens over the past month are here to stay. Oak Grove station, which was reopened to support usual Orange Line passengers during the disruption, will remain in service and become a regular stop on the Haverhill Line in Zone 1A. Additionally, some of the services added at Forest Hills will remain, ensuring two trains come moving inbound every weekday morning at the station.

“During the Orange Line service disruption, we welcomed many new riders to the commuter rail,” said Abdellah Chajai, CEO of Keolis Commuter Services. “We hope that they found their trips to be reliable and convenient and that they will continue to see the commuter rail as a great option for their transportation needs.”

Boston Mayor Michelle Wu, who rides the Orange Line from her home in Roslindale to Boston City Hall, said at a press conference that her ride “sitting in a shiny new train” on Monday morning went “pretty smoothly.”

She said her commute was shortened without having to worry about shuttle buses and transferring to the Green Line. The ride took about the same amount of time, if not a little shorter than before the shutdown, she said.

Orange Line trains are still moving slowly over the six repaired slow zones, Poftak said, for the next week as the MBTA tests the new tracks and trains.

“I think starting next week we’ll see a big difference,” Wu said.

Wu reminded GBH Radio listeners last week that major problems with staffing the T will take time to address.

“One big key thing that has not been resolved and will take some time to resolve is staffing levels,” she said. “When the T is so short on positions like signal dispatchers and others that control the trains, it will still take some time to build that workforce to be able to run at full strength.”

Baker said Sunday that hiring is a “primary objective” at the T, as well as implementing the Federal Transit Administration’s safety recommendations.

“The T’s primary objective in the short term needs to be to deal with the issues in their roadmap, and to hire the many, many, many people who currently have unfilled positions that are in fact funded,” he said.

The Legislature and Baker have recently agreed to pour hundreds of millions of dollars in one-time funds into the T and Baker deflected Sunday when asked about adopting new revenue sources for the T.

“I think the T’s finances for the next several years are actually in pretty good shape,” Baker said, adding that “no one knows where ridership’s going to be, that’s going to be the biggest question of all.”

Budget-writers at the T for months have forecast the agency will face an operating budget shortfall of hundreds of millions of dollars once it exhausts all remaining one-time federal pandemic aid, and the need for additional funding is bound to grow if the MBTA seeks to bulk up its workforce or launch a maintenance blitz following the FTA’s review.

“We all know it is going to take more money, and we can see that we have lots of other financial challenges,” MBTA board member Mary Beth Mello said about the FTA directives last week.