From CommuterPages:
Bike access will remain open on the sidepaths of the Key, Roosevelt, and 14th Street bridges. These bridges have narrow sidepaths which may make riding difficult with the heavy pedestrian traffic that is expected. Memorial Bridge on the other hand will be open only to bicyclists and pedestrians - and closed to all motor vehicles - so this bridge is recommended for bicyclists as the there will be more room for riding.
Source:
http://www.commuterpageblog.com/2009...the-bicyc.html
This is good advice; I'm planning on doing the Memorial Bridge. The Roosevelt Bridge is more convenient for me, but its narrow sidewalk can make a ride frustrating on a normal day -- I can't imagine the madhouse of inauguration day.
A gentle scolding is due to DC area media who made me panic yesterday by reporting all bridges would be closed to "private vehicles." They meant "private motor vehicles."