The Orange Line will shut down for 30 days starting at 9 p.m. on Fri., Aug. 19, the MBTA said last week, setting off hurried preparations for shuttle buses, expanded scheduling of commuter rail stops, and other management efforts to blunt the impact of closing a line that typically carries more than 100,000 people every weekday.

The repairs involve track replacement and signal upgrades.

“It will be chaos,” Mayor Michelle Wu acknowledged Tuesday, as her administration is working with the T to create bus-only areas within the city’s borders.

“Chaos” is a mode to which the MBTA and its riders have become accustomed over the last year: An Orange Line car caught fire while on a bridge over the Mystic River, forcing passengers to spill out onto the tracks, and in the case of one woman, dive into the water; a Red Line rider died after his arm was caught in a closing door; and a spate of derailments and collisions. Most recently, a bus caught fire in Jamaica Plain on Aug. 4 and sent two workers to the hospital for smoke inhalation.

Federal transit safety officials, while taking a closer look at the T’s operations, have mandated cuts to frequency of subway service, due to the lack of available dispatchers. The agency is seeking to hire more people, but it faces the same economic headwinds hitting other sectors that are scrambling to hire more people. The drop in subway frequency could last into 2023.

The Orange Line closing is unprecedented. “We have never shut down an entire line in this way in order to make sweeping improvements, but we’re doing this because it’s the fastest, most efficient way to deliver the benefits to our customers,” Steve Poftak, the T’s general manager, told reporters.

When the line returns to service, most of the cars will be brand new, assembled in a Springfield factory by a Chinese-owned company.

Additionally, the agency’s Green Line is getting its own shutdown, due to the construction of a downtown office tower. Service between Government Center to Union Square in Somerville will be replaced by free shuttle buses between Aug. 22 and Sept. 18, overlapping with the Orange Line’s closure.

Is the Red Line, which has a trunk running through Dorchester and connecting to a trolley line ending in Mattapan, next? MBTA officials left the door open. “We reserve the right. I think this is something we’re going to work on in real time,” Poftak said.

On Monday, during an appearance with US Sen. Ed Markey to promote the benefits of legislation seeking to invest in clean energy while tackling the highest level of inflation in 40 years, Wu blamed the state of the MBTA on decades of delayed action and little maintenance, “starving” the system while it was saddled with debt from the $24 billion Big Dig project.

“This is not an ideal situation by any means,” the mayor said. “And we never should have gotten to this point.” Added Markey: “We just have to spend the money and use all our technological capabilities in order to get this fixed once and for all.”

Over the last seven years, the Baker administration has sought to spend on capital upgrades, but what they have appeared to lack is enough time to fix everything, given the preceding decades of lagging maintenance.

In one recent example from last month, the MBTA’s oversight board, appointed by the governor, signed off on a contract for the expansion and improvement of Codman Yard as the agency prepares for a new fleet of Red Line cars, assembled by the aforementioned factory in Springfield.

The expansion of Codman Yard, which is bounded by Gallivan Boulevard, Hillsdale and Hutchinson streets, will increase storage space for the fleet vehicles, adding six new tracks, security cameras, and other additional infrastructure.

Barletta Heavy Division Inc. won the contract after putting in a $85.9 million bid for the job and beating out three other companies.

Even with all the attempts at mitigation measures and MBTA officials pledging safety upgrades, there continues to be talk of a federal takeover. Rep. William Straus, a Mattapoisett lawmaker who co-chairs the state Legislature’s Transportation Committee, raised the prospect in an interview with Axios Boston.

Both Wu and Markey say they oppose such a move. “We need a partnership, not a takeover,” the mayor said. “The situation is at a breaking point when riders don’t know on any given day what might come up, how serious of a safety concern might emerge that day, how late they will be that day. It is time for sustained focus, investment and action to tackle what we’ve known for many, many years has been a building problem.”

Wu and Markey are in agreement on another proposal: Make the entire MBTA system free during the Orange Line shutdown.

“The Baker Administration and the MBTA’s decision to shut down the entirety of the Orange Line for an entire month is devastating, especially for the Black, brown, disabled, low-income, and other marginalized communities who depend on the Orange Line to get to work, school, the grocery store, and access other critical services,” Markey and US Rep. Ayanna Pressley said in a joint statement last week.

The state can afford the free-ride proposal due to federal relief through Congressional appropriations, Markey and Pressley contend.

Asked about the Markey-Pressley statement, a spokesman for the transit agency said, “The MBTA understands and appreciates that this diversion will be an inconvenience for commuters, and that’s why the T is working closely with its municipal partners to develop viable and effective alternatives. No fares will be collected on the shuttle buses that will operate throughout the length of the diversion.”

According to Wu, twice as many commuter rail trains than normal will be stopping at overlapping Boston stops along the Orange Line to take people in and out of the city.

Another MBTA shutdown will overlap with the Orange Line closure, if temporarily. For one day, Saturday, Aug. 20, Fairmount Line service between Readville and South Station will be halted due to the planned demolition of the Jones Avenue pedestrian overpass. Buses will replace train service, with service expected to return on Sunday, Aug. 21.

The T’s schedule notes that travelers on the south side of the Orange Line and to downtown can take the Needham Line, which stops at Forest Hills, Ruggles Street, Back Bay Station, and South Station, while riders on the north side can take the Haverhill Line, which stops at Oak Grove, Malden Center, and North Station.

Customers will be able to show a CharlieCard or other MBTA pass to the conductors to signal they are seeking to avoid the Orange Line disruption, so the commuter rail will “essentially be free as well,” the mayor said.

“Any mechanism that we can have to ensure that we’re removing barriers goes a long way,” said Wu, who has pushed for a fare-free MBTA system and made it a key plank in her 2021 mayoral campaign platform.

Material from State House News Service was used in this report.