Generally bike is the best way to get to any kind of big event downtown. It may still be for the inaugural, although this will be an event unlike any before. The current talk is 4 million people, which would be at least three times bigger than any event in the city's history. If that's the case, you probably won't be able to get within a mile of the Capitol on a bike. Be prepared to walk. There is virtually no bike parking on the Mall, so I would bring a cable so you can lock to something non-traditional.

That said, I think every other mode of transportation is going to be far worse. They're urging people to take the subway, but the all-time one-day ridership record for the subway is about 850,000. They're not going to allow parking anywhere near the Mall.

I'll be biking down there, wouldn't miss it for the world.