Most of BART’s new rail cars will soon be built in east Contra Costa County, giving a boost to the area’s struggling industrial economy and speeding delivery of the transit agency’s future fleet.

Bombardier, the Canadian company building the transit system’s Fleet of the Future, plans to open an assembly plant at a large industrial site off of Loveridge Road in Pittsburg. The company expects to hire about 50 people to help assemble the cars.

Work on assembling BART’s 775 modern rail cars, which is currently done in upstate New York, is expected to move to Pittsburg within months, Bombardier Americas President Lee Sanders announced at a news conference in the warehouse Friday.

“We will be transferring these jobs to California,” he said, standing in front of a shiny new BART car sitting on a truck trailer.

Bombardier has produced 89 of the new rail cars at its assembly plant in Plattsburgh, NY, and delivered them to BART’s Hayward yard by truck. Social media photos of BART cars rolling across the Great Plains are not uncommon on Instagram, Twitter and Facebook.

Beginning in September those rail cars — with three doors, video screens, automated announcements and brightly colored interiors — will be assembled in Pittsburg and delivered to a Bart yard.

Eighty of the new cars — enough to make up eight full-length trains — are in service, and they’ve been popular among commuters who appreciate the cleaniness, the functioning air conditioning and heating sytems and the new-car look and feel. But the cars have also been behind schedule in arriving to the Bay Area and being placed on the tracks.

BART’s initial plan was to replace and slightly expand its existing fleet of 669 rail cars, many of them more than 40 years old, by 2022 but that date has been pushed back to spring of 2023. By now, BART was supposed to have 176 cars on hand.

Sanders said Bombardier has picked up the pace on delivering new cars, and is now on schedule. But building the trains in the Bay Area “should certainly help with reducing delays,” he said. “This way we’ll make it in the Bay Area for the Bay Area.”

And with Bay Area workers. Politicians from east Contra Costa, a historically industrial area, hailed the new jobs, hoping the 50 new positions at Bombardier would grow, and also attract other manufacturers to their part of the Bay Area.

“This means local jobs and continued growth of our manufacturing base here in Pittsburg,” said Mayor Juan Banales. “Hopefully it acts as a catalyst to create more jobs locally.’

BART and Contra Costa leaders worked together to help lure Bombardier to the plant, which was also used when the transit system overhauled its original rail cars in the late 1990s. The state helped to lure the rail manufacturer with $1 million in California Competes tax credits that will be paid out over five years, said Maryanne Roberts, a Bombardier spokeswoman.

Michael Cabanatuan is a San Francisco Chronicle staff writer. Email: mcabanatuan@sfchronicle.com Twitter: @ctuan