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Metro Stop on Campus
The Metro will be your best friend during your time at CUA. It is one of the two DC schools blessed to have a stop right on campus. Fares are reasonably low if you're heading into the center city, and almost all major attractions are accessible via the system (huge exception: Georgetown). You'll have to put up with bumps, delays, and poor customer service, but it'll get you from point A to point B.
There's also a new Capital Bikeshare stand near campus. You can rent a bike by the hour and return it at any Bikeshare location in the city. DC is a very cyclist-friendly town; the new Metropolitan Branch Trail, which will extent from Silver Spring to the Capitol when it's completed, goes right past campus.