SEPTA began running shuttle buses Sunday between Norristown and Bridgeport in place of M service, to allow crews to begin a $55 million bridge restoration project.

The Bridgeport Viaduct carries the M, also known as the Norristown High Speed Line, over the Schuylkill River. It will be shut down until May 9, with future closures planned later this year and in early 2027 to complete the work.

Buses will only be needed between Norristown Transit Center and the Bridgeport stop, with trolleys running normally from there to 69th Street Transit Center.

A schedule incorporating the shuttle service is posted on SEPTA’s website. The adjustment should only cost commuters an extra 6 minutes, according to the authority’s general manager, Scott Sauer.

SEPTA officials said the project will impact a third of the M line’s 5,600 weekday riders who travel to and from Norristown.

“The project is a significant commitment at a time when our capital budget is severely constrained, but it’s an investment that we must make,” SEPTA Board Chair Kenneth E. Lawrence Jr. said at a news conference Friday in Bridgeport.

Constructed 115 years ago, the viaduct is 3,525 feet long, making it the third-longest bridge in the SEPTA system, officials said.

Contractors will be assessing and repairing the concrete abutments that rise out of the river, along with the steel structure of the bridge. A concrete deck and maintenance catwalk will be replaced, according to SEPTA. The project also includes repainting the viaduct and redoing a stairwell at the Norristown station.

“What this kind of work does for us is it ensures that we never get to a place where we have to stop running service on this bridge,” Sauer added.

The viaduct was closed for four months in 2013 for emergency project track tie and timber replacement; however, Sauer said the structure has not undergone a significant rehabilitation since 1985.

SEPTA leaders said they want to do the restoration in phases and reopen the bridge in May to allow uninterrupted M service for the FIFA World Cup, MLB All-Star Game and festivities surrounding the nation’s 250th birthday over the summer.

Future viaduct closures are scheduled to take place from Aug. 1 to Dec. 19 and from Jan. 18 until Feb. 6, according to the authority’s website.