From WABA:

Rock Creek Parkway's Hiker-Biker Trail to Close
from Virginia Avenue to the P Street Ramp

As part of the ongoing road construction project on Rock Creek Parkway, the National Park Service (NPS) will begin a closure of the hiker-biker trail on the Parkway. Beginning Monday, March 10, 2008, and for approximately four weeks, the trail will be closed from Virginia Avenue to the P Street ramp in both directions. Construction detour signs will be in place to direct the walking, hiking and biking public around the construction zone and will direct any visitors along an alternate route through various streets in Georgetown. Variable message boards and construction signs are in place to alert the public of the expected closure. Inclement weather may require adjustments to the schedule. The NPS will continue to inform the public and the media of any adjustments in the work schedule. Every effort is being made to minimize traffic delays and accomplish the work in a timely manner.