The diversions will make way for bridge work under the Red Line tracks, which will also result in sections of the track being removed and replaced with new tracks over the course of the construction work.

The Red Line will be replaced by shuttle buses between Park Street and Kendall/MIT stations, most weekends between Sept. 29 and Dec. 17. The Longfellow Bridge will be closed to inbound cars from 11 p.m. on Fridays until 5 a.m. Mondays. Car traffic to Cambridge was already barred during much of the rehabilitation project.

As the state sprints to finally finish rehabbing the historic Longfellow Bridge, Red Line trains will be replaced by buses over the Charles River and passenger cars will be barred from crossing the bridge nearly every weekend this fall.


After nearly five years of disruptions — including other long periods where weekend Red Line service over the bridge was interrupted — the Longfellow is expected to reopen to all traffic next May, according to Massachusetts Department of Transportation spokesman Patrick Marvin.

Plans to rehab the century-old bridge, best known for its “salt-and-pepper shaker” towers, had been years in the making before finally beginning in 2013.

And its reopening next spring will be more than 18 months later than originally planned, a delay that was expected to boost the project’s price tag. It’s partially due to the challenges of rebuilding portions of the bridge with construction techniques rarely used today, like riveting — all part of an effort to maintain the structure’s historic character.

The Longfellow Bridge will come back online around the same time as another Charles River crossing to the east, the North Washington Street Bridge, is scheduled to shut in parts for a long-term replacement project. The Longfellow project also includes a new pedestrian footbridge connecting the Esplanade to Beacon Hill over Storrow Drive.


During this latest set of Longfellow shutdowns, T riders and drivers will get a reprieve during just two autumn weekends: when the Head of the Charles rowing race, expected to draw large crowds, returns Oct. 21-22; and Thanksgiving weekend, Nov. 25-26.

The schedule could change, however, depending on weather.

Cyclists, pedestrians, and emergency vehicles will still be able to cross the bridge during the weekend closures. The MBTA shuttle buses will stop at Charles/MGH Station en route to Kendall/MIT and Park Street.

The weekend work might also affect the Monday morning commute on the Red Line: The newly laid track may require the MBTA to set speed restrictions on trains, the Transportation Department said.

Adam Vaccaro can be reached at adam.vaccaro@globe.com. Follow him on Twitter at @adamtvaccaro.