This is from The Washington Post (the map is great):
The bad news: Witnessing this historic occasion in person will require a bit of a schlep. The good news: Officials say pedestrians will be allowed to go just about everywhere. So what about those who have to park their cars and venture over the Potomac and Anacostia rivers on foot for the first time? Put on your sturdy shoes, grab a wind-resistant jacket and climb down into this guide to walking over the 10 bridges into the District of Columbia.