Account-Based Ticketing (ABT)

Account-based ticketing (ABT) is a fare collection model for public transport in which the record of a passenger's journeys and entitlements is kept in a central back-office account rather than on the ticket itself. The passenger taps a contactless bank card, a phone wallet or a transport-issued card at a reader; the reader simply identifies the account, and the fare is worked out centrally, often after the day's travel is complete.

ABT replaced older card-based systems, in which the fare and the remaining balance were written onto a smart card in the passenger's pocket. Transport for London's acceptance of contactless bank cards and New York's OMNY system are well-known examples. Where passengers pay with their own bank cards, ABT relies on open-loop card payments, so transit operators act as merchants subject to card scheme rules.

Think of a bar tab. Instead of paying for each drink as it is poured, you show your card once, the bar keeps a running list, and at the end of the night you pay one bill. The bar can also apply a rule such as "never more than a set amount for the evening".

Account-based ticketing runs public transport the same way. Each tap at a gate or on a bus adds a line to the passenger's tab in a central computer. Overnight, the system adds up the journeys, works out the cheapest fare that applies, and charges the card once. The card is just a key to the tab, not a wallet holding the money.

1. The passenger taps a contactless card or phone on a validator at a gate or on board, using near field communication.
2. The validator reads a card identifier, often a token derived from the card number, records the time and place, and decides in a fraction of a second whether to let the passenger through, using a local list of blocked cards.
3. Taps are sent to the back office, which links entry and exit taps into journeys.
4. The back office applies fare rules, including capping, and sends one aggregated charge per day or period to the transit operator's acquirer.
5. The passenger can see their journeys and charges online, and inspectors check validity by reading the same card.

Gates must open in well under a second, which is too fast for a normal online authorisation. Card schemes have therefore created transit-specific transaction models. A validator typically checks the card offline and lets the passenger travel, while the system sends a small authorisation or account check to the card issuer in the background. Fares are then aggregated over a period and submitted as one transaction. If the card turns out to be invalid or declined, the operator places it on a deny list until the debt is paid. The risk that the first journey is not paid, often called first ride risk, is shared between operators and the card schemes under their rules.

Because passengers use their own debit and credit cards or mobile wallets, the operator no longer has to issue and top up as many travel cards, and visitors can ride without buying a local ticket. A transport authority can still issue its own card, which works within the same account system but is a closed-loop product that only works on that network.

Central calculation makes fare capping possible: once a passenger's charges for a day or week reach the price of a travel pass, further journeys in that period are free. This gives the benefits of a pass without having to buy one in advance, which matters for people who cannot afford a large upfront payment. ABT also makes it easier to change fares, add concessions, and link transport with other services such as bike hire under one account. It largely replaces paper tickets and stored value balances that passengers can lose.

• Privacy. The back office holds detailed records of where and when people travel, which raises data protection questions about retention and access by authorities.
• Inclusion. People without bank cards or smartphones need an alternative, usually a transit-issued card bought with cash.
• Card clash. A reader can charge the wrong card if a passenger taps a wallet holding several contactless cards.
• Cost and complexity. Back-office systems, contactless validators and card acceptance fees are expensive, and operators remain responsible for meeting PCI DSS security standards and scheme rules.