The MBTA will completely replace the Red Line subway fleet, spending up to $280 million to put all new vehicles into service by 2024.

In 2014, the MBTA purchased replacements for the two oldest sets of Red Line cars, which dated back to the 1960s. Those cars will be delivered in 2018. Monday's decision means the purchase of 120 additional replacements for the most "modern" set of Red Line cars, the 1990's vintage. China-based railroad manufacturer CRRC has the contract to manufacture all of these.

MBTA officials say standardized vehicles can move and brake faster, allowing more frequent service and improving capacity by 50 percent when the line is entirely modern in eight years.  Trains traveling between stations faster can move approximately 10,000 more passengers per hour, according to the MBTA. That's an overall increase of 50 percent.

Pollack told reporters the purchase is an attempt to rethink how the MBTA operates on large scale projects and how it thinks about its own future. Beyond figuring out the minimum number of vehicles the T needs to buy to keep itself running, or how to patch the system up through overhauling equipment, Pollack wanted to focus on the objectives of the transit line first.

"What we're trying to ask is what kind of system do we want to be running in the year 2025? How many people need to use the Red Line?" Pollack said.

"And how do we buy a Red Line that not only [is] a good purchase, but the folks who are going to be in charge of maintaining that system in 2025 and 2030 and 2035 have a uniform fleet with uniform parts that they can do life-cycle maintenance on and upgrade as technology improves," Pollack added.

The T has enough funding through state and its own bonds to make major purchases like this and pay them off over time, but some MBTA riders were still worried about the operation budget of the agency, with faces a potential $110 million budget gap for next year.

"Whether it can help with the financial stresses they've had for year, I don't know if that would affect it, but newer trains, I'm going to assume would be better," John Killilea, a commuter from Quincy told WGBH News at Park Street Station.

Many regular T riders hadn't heard that new cars are on the way, but seemed hopeful that improvements would aid their commutes.

"Let's say on the days you're really in a hurry, it always breaks down. It's always bad and stuff like that," said Jackson Joseph, 16, of Dorchester, who takes the Red Line and Silver Line to Cathedral High.

MBTA managers briefed reporters Monday before the board's vote. Acting MBTA General Manager Brian Shortsleeve and Transportation Secretary Stephanie Pollack defended the decision to directly increase the order from CRRC instead of going through traditional procurement processes, saying that an open procurement would delay the order by over two years and cost more to keep old trains in service for that time.

The T negotiated a deal with CRRC to manufacture an additional 120 cars at $1,850,000 apiece, totaling $222,000,000. That price, they say, is actually $40,000 lower than the price agreed upon in 2014 for the current order of 58 cars.

The existing purchase will have new Red Line cars in service by 2019. The T expects today's order of cars to be delivered from June 2022 through September 2023, coming into service in 2024. 

The T chose to buy new cars instead of paying even more to overhaul existing vehicles from the 1990s. Keeping those 1990s-era cars in service a little bit longer without overhauling them as planned will cost the T an expected $36.46 million in maintenance.