Apart from some tourist buses, all bus services in Dublin are one-person operated, and daytime fares are determined by the number of fare stages travelled through — fares are payable in coin and only the exact fare is acceptable — if passengers overpay they will not receive change. A cheaper alternative to cash is a Leap card loaded with a cash balance or a weekly or other pass. This can be bought from Dublin Bus or its agents. Flat fare journeys are processed by a validating machine on the right of the entrance door of the bus. When the fare for the journey is to be determined by the number of stages to be travelled, the validating machine on the left of the entrance door should be used and the driver informed of the destination to avoid overdeduction from the cash balance on the card. Nitelink buses charge a €6.60 flat fare (€4.50 on Leap) regardless of the distance travelled. The Leap card, introduced in December 2011, is a smart card that can be used on Dublin Bus, DART, suburban rail services in the Dublin area and the Luas.