The project eventually will put a deck over the Third Street Tunnel south of Massachusetts Avenue.

The project that will put a deck over the Third Street Tunnel south of Massachusetts Avenue NW is entering a new phase this week, affecting travel in the central part of the District.

The work involves the relocation of utilities along Massachusetts Avenue and H Street NW, between Second and Fourth streets, a phase likely to continue for four months. Traffic on H Street will not be allowed to travel west past Massachusetts Avenue between Third and Fourth streets. Drivers will be directed onto Massachusetts Avenue, then to turn left on Fourth Street toward the continuation of H Street.

This area is an important — and confusing — junction for commuters, whether they drive, bike or walk. It’s a tricky crossroads, and the lengthy construction will make it even trickier.

Third Street Tunnel The chasm on I-395 below Massachusetts Avenue will eventually be covered. (Robert Thomson – The Washington Post)

During this phase, construction is scheduled for 7 a.m. to 7 p.m. and 8 p.m. to 6 a.m. On Saturdays, work may occur between 8 a.m. and 8 p.m.

During the day, lanes may be closed temporarily throughout the work area. Watch for flaggers redirecting the traffic.

At night, drivers may encounter detours around temporarily closed intersections. Those would occur between 10 p.m. and 5 a.m.

Pedestrian access will also be restricted within the areas from westbound H Street to Third, Fourth and H streets; Fourth Street and Massachusetts Avenue; northbound Third Street at H Street; and the north side of Massachusetts Avenue between Second and Fourth streets. The Metrobus X2 and 80 stops on H Street between Second and Third streets have also been eliminated.

This area west of Union Station is going to look very different over the next several years. The new deck over the interstate will serve as a foundation for a development project called Capitol Crossing.