From the Getting There blog:
The State Highway Administration will begin about three weeks of overnight closures of the westbound Beltway at Charles Street tonight to let it install structural steel beams for a new bridge.
Crews will begin the closures Sunday through Thursday nights at 8 p.m. by taking away a single lane. They will close a second lane at 10 p.m. and the remaining lanes from 11 p.m. through 5 a.m.
Traffic will be diverted at Exit 25 to the Charles Street interchange and the roundabout at Charles and Bellona Avenue before rejoining Beltway traffic beyond the bridge area. The eastbound Beltway will have two lanes closed, and the ramp from northbound Charles to the westbound Beltway will be detoured through the roundabout. Closings and detours will be suspended on weekends.
The work is part of the SHA's $43.6 million project to replace the half-century-old Charles Street bridge with a modern, wider structure. The project is expected to be completed in the summer of 2012.