Timeline: How the MBTA's deal to replace Red and Orange Line cars went off track

The MBTA is 11 years into a contract to replace its aging subway cars on the Orange and Red lines. Hundreds of the promised trains are overdue.

In 2014, the transit agency signed a contract with the China Railroad Rolling Stock Corporation, known as CRRC, to build hundreds of new cars. All trains were supposed to be delivered by 2023.

But over the past decade, the project has been riddled with challenges causing delay after delay — and a ballooning price tag. The most recent estimate is that Orange Line cars will be delivered by the end of 2025 and all Red Line cars in 2027. The project's cost has swelled to $1 billion overall.

How did the plan go so off the rails?

Here is a timeline of the MBTA's contract with CRRC. While this is not the entire picture, it gives context to the setbacks and successes in the agency's effort to upgrade America's oldest subway system.