DC Metro User's Guide
Paying for Your Trip: SmarTrip Cards and Farecards
Fare machines, found at every station in the DC Metro system, allows you to purchase a new Farecard, or add money to an existing Farecard or SmarTrip card. Some stations will allow you to purchase SmarTrip cards as well.
Before reaching the platform of each metro station, you must buy either a Farecard or a SmarTrip card. Farecards are paper tickets with a magnetic strip. The newer SmarTrip card is a proximity card. You can load money onto each type of card, and use them to pay when you enter and exit a DC Metro station.
A Farecard can be purchased at any metro station from a machine like the one pictured here. Purchases can be made with cash or a credit card. You need to use the same SmarTrip card or Farecard to enter and exit the system, and you must have one per person or Metro will charge you the maximum fare. Additionally, if you do not have funds to exit, you'll need to load more money onto your card at an Exitfare machine. Be careful; these machines, found near each exit, do not take credit card payment. You'll be best off if you keep your balance from getting too low.
SmarTrip cards can only be purchased at terminus stations or the Metro Center station, online, or from select retailers including CVS and several grocery stores.