Recently, if you look out the windows on the Red Line between Harvard and Porter, you'll almost always find workers pressing against the wall to let a train by. In case the water-stained tunnel walls don't give it away: they're working on the corroded tracks as we speak. However, that may not be enough time to keep the tunnels in shape, and as The Globe explains:
The MBTA will close the Red Line north of Harvard Square on weekends from November through March to complete $80 million in repairs designed to keep trains from derailing, transit administrators said yesterday.
Starting Nov. 5, weekend service will stop to allow T crews to plug tunnel cracks and seal water leaks that have eroded the concrete track base and corroded power lines. Then crews will replace damaged track, supports, and electrical components.