FOR THE NEXT SIX WEEKENDS, the MBTA is shutting down seven downtown stations on the Orange Line to replace track and complete cosmetic and signage improvements at four of the stations.

Between Sullivan Station and Tufts Medical Center, the Orange Line will shut down starting at 8:45 p.m. Friday night and reopen in time for the start of service Monday morning. The same shutdown process will be followed for the next five weekends.

Steve Poftak, the general manager of the T, said the Orange Line weekend shutdown is the biggest the T has ever attempted, but he warned it will be followed this fall by weekend shutdowns on the Red and Green Lines and possibly weekday shutdowns on some subway branches next year.

Gov. Charlie Baker greenlighted these types of repair projects this summer after the derailment of a Red Line train. He said the pace of investment in the MBTA was moving too slowly by doing most of the work at night when the system isn’t running.

Poftak said overnight projects allow only about two-to-three hours of work after accounting for setup and takedown time. He said the Orange Line weekend shutdown will allow for about 50 hours of uninterrupted work, enough to finish projects that would normally take months or a year working during overnight periods.

The T has a fairly complicated replacement service set up to accommodate passengers during the shutdown. Passengers headed toward Forest Hills on the Orange Line will be directed to get off at Sullivan Square and board shuttle buses to Haymarket, where they will take the Green Line to Copley and then walk two-tenths of a mile to Back Bay Station where they can get back on the Orange Line.

Poftak said he didn’t know how much longer the replacement service would take, but he said customers should allow at least 20 to 30 minutes extra. He didn’t know how many passengers will be affected by the Orange Line shutdown, but he said it would be a “significant” number.

Most of the work over the next six weekends will be at the Downtown Crossing, Haymarket, State, and Chinatown stations. The shutdown extends to Sullivan Square because the T will be bringing track and other equipment into the subway tunnels there. The T hopes to replace an estimated 2,250 feet, or four-tenths of a mile, of track.

Ferry customers get airport security perk

The Massachusetts Port Authority is now giving passengers who take a ferry or water taxi to Logan International Airport tickets that allow them to skip to the front of the security check-in line.

The special tickets were first introduced on the Massport bus shuttle service between Back Bay and the airport. The security perk, combined with a sharp drop in the fare (from $7.50 to $3 going to the airport and free from the airport to Back Bay), helped double passenger traffic on the shuttle during its first four months of operation.

Massport now wants see if the security perk alone can increase ridership on the MBTA ferries and water taxis operating between the airport and Hingham and Hull.