Most Metro stations do not allow overnight parking. According to metro's website at www.wmata.com, Greenbelt is one of the three stations where you are allowed to do that. Also don't forget that you will need a Smartrip card in order to exit the station parking. There is no order way to pay for parking and you can get a smartrip card at the metro center sales office inside the station or you can purchase a card online.

Multiple day parking is available at three stations: Greenbelt, Huntington and Franconia-Springfield. Each of these stations has between 15 and 17 spaces allocated for multi-day use, which are available on a first-come, first-served basis.