I just went to the Udvar Hazy museum during an extended layover and the shuttle over there worked great. It's still $0.50 and you get it outside of the main terminal area at loading point 2E (it's the row where you'll see all the rental car buses picking people up). The shuttle leaves the airport at 15 past the hour, from at least 10-3, but it could be longer. There are returns at half past the hour right where it drope you off at the museum. I'd advise on planning at least hours at the museum and avoiding bringing anything more than a backpack. I was there almost 3 hours and I could still go back for another hour, so you might want to plan on visiting over the course of 2 layovers. Other than that, it's a fantastic museum with some amazing planes, and getting there was very easy. This is a fantastic way to spend an extended layover.