Embodiments of the present invention relate to an electronic payment system and more particularly to a unified transportation payment system. In one embodiment, a passenger uses a card which has been set up for use within the transportation system to pay transportation costs. The card contains data including information representing a monetary value. The passenger uses the card at a card reader located at the transportation center. The card reader includes an application programming interface (API) which receives the data read from the card including information representing the monetary value stored on the card. The monetary value is adjusted by assessing an amount corresponding to a value associated with the transaction.