The major work for this weekend will occur on the Red Line, but Metro also plans maintenance on the other four lines, which will disrupt travel for many riders. All work is scheduled to start at 10 p.m. Friday and continue through the rail system’s midnight closing on Sunday.

Red Line: Free shuttle buses will replace trains between Bethesda and Grosvenor. The Medical Center station will be closed. Workers are replacing track circuits along the line.

The transit authority says trains will operate on a normal weekend schedule between Shady Grove and Grosvenor and between Bethesda and Glenmont. But riders passing through the work zone should expect delays of about 20 minutes on their normal travel times.

On Friday night, the last Glenmont-bound train to operate before work begins will leave Shady Grove at 9:43 p.m. and Bethesda at 10 p.m. The last Shady Grove-bound train will leave Glenmont at 9:05 p.m. and Bethesda at 9:50 p.m.

The last Red Line train from Shady Grove will leave 15 minutes earlier than usual, at 2:15 a.m. Saturday and Sunday. (That’s the night owl service from Friday and Saturday nights.) The last train on Sunday night will leave at 11:15.

The shuttle bus services work pretty well, since Metro has a chance to organize them in advance. (It’s the bus bridges the transit authority arranges in haste to deal with emergencies that lead to confusion and complaints among riders.)

However, they do require riders to leave the stations and get out into the weather. The Capital Weather Gang says there’s a good chance Saturday will be rainy, with a smaller chance of showers on Sunday. The high temperatures both days should be in the mid-40s.

On the other four lines, trains will be sharing tracks around work zones.

Orange Line: Trains will share a track between East Falls Church and West Falls Church and between Stadium-Armory and Cheverly. Trains are scheduled to leave the ends of the line at Vienna and New Carrollton every 24 minutes.

Metro says service will be coordinated with the Blue Line to provide trains every 12 minutes at stations from Rosslyn to Stadium-Armory, the tunnel segment used by both lines.

Blue Line: Trains will share a track between Braddock Road and Van Dorn Street. They will leave the ends of the line at Franconia-Springfield and Largo Town Center every 24 minutes, Metro says.

Green Line: Trains will share a track between Naylor Road and Branch Avenue. They will leave the ends of the line at Greenbelt and Branch Avenue every 24 minutes. Metro says more trains may enter service based on the ridership and track space.

Yellow Line: Trains will share a track between Braddock Road and Huntington. They will operate between Huntington and Mount Vernon Square every 24 minutes. More trains may be added based on ridership and track space.

Riders who want to go north of Mount Vernon Square to stations including Fort Totten and Greenbelt should switch to a Green Line train on the same platform..