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At long last, the Red Line is slow zone-free.

The MBTA announced last week that the last remaining slow zones along the Red Line would be eliminated by Monday, when the Harvard to Broadway section of the route comes back online following a weeklong shutdown for maintenance.

The shutdown, which flooded Harvard Square with wall-to-wall shuttle buses, marks the final step in a yearlong improvement process to eliminate slow zones across the Red Line — stretches where speed restrictions allow trains to move, albeit slowly, over decrepit segments of train track that might otherwise have posed a safety risk to riders.

Those included an infamous slow zone between the Harvard and Central Square T stations, where a one-mile trip that takes two-and-a-half minutes at full speed lasted up to seven. That slow zone was eliminated at the end of July.

The improvements, launched late last year, span the T’s main four subway lines. The Orange Line reached a similar milestone last month, and the Green Line is expected to do so in December.

“At the end of the day, it’s not just about removing the restrictions,” MBTA General Manager Phillip Eng said at an MBTA board of directors meeting on Thursday. “It’s about giving the riders, the public, improved service — that reliability that they count on.”

Seth Kaplan, who oversees data tools for the Massachusetts transit advocacy group Transit Matters, praised the T for having “made good on their promise to get rid of every slow zone this year.”

“We have to applaud them for that,” he said. But he cautioned that the T was not yet in the clear.

The Federal Transit Administration threatened to take over the T in mid-2022 after it discovered serious flaws in the T’s safety producers and maintenance. Since then, the system has experienced accidents, service cuts, and chronic delays, leading transit advocates to declare the system in crisis.

Even as the T has begun to rehabilitate its public image — installing Eng as a new general manager and embarking on the yearlong service improvement project — billions worth of deferred maintenance remains to be finished.

Eng said at the Thursday board meeting that partial shutdowns — mostly confined to weekends — would continue next year to upgrade signaling systems and to keep track in “a state of good repair.” But he added that the shutdowns “won’t be to the level that we had this year.”

Shutdowns on the Red Line have proved an enormous disruption throughout Cambridge this year, sending tens of thousands of riders above ground for weeks at a time. The added traffic of the replacement shuttles and a rise in commuters opting for buses or cars have clogged Massachusetts Avenue and increased travel times across the city.

The coming year for the T faces a looming budget crisis. The T has been underfunded by the state legislature for decades but lower post-pandemic ridership, pay hikes for its workers, and the cost of this year’s track maintenance and shutdowns have worsened the problem.

Advocates say only a new, long-term source of funding can fill the $700-million hole — like new tolls, increasing the gas tax or car registration fee, or even congestion pricing, which New York officials are set to institute in January.

The last time the T faced a budget crisis, in 2021, it proposed eliminating 25 bus routes, as well as weekend and evening commuter rail service, and reducing the frequency of buses and trains. In the coming fiscal year, the T’s budget hole is poised to be five times larger than it was in 2021, meaning more extreme service cuts are possible.

Kaplan cautioned the state not to “kick the can down the road.”

“This is now a time to think big,” Kaplan said.

—Staff writer Jack R. Trapanick can be reached at jack.trapanick@thecrimson.com. Follow him on X @jackrtrapanick.