Transport for London is celebrating the successful implementation of contactless card payments on all of London's 8,500 buses.

Since the service was launched in December 2012, more than 6.5 million London bus journeys have been paid for using contactless American Express, MasterCard or Visa Europe contactless payment cards, the U.K. transit operator said.

Contactless open-loop cards can be used in addition to TFL's existing proprietary contactless Oyster cards, if customers don't have an Oyster card or have run out of credit on their Oyster card. Tickets bought with contactless cards cost less than cash tickets.

TFL said it will launch contactless card payments in its wider transit network in 2014 for journeys on over-ground and underground trains. Following the full rollout, TFL said it will become one of the world's largest single merchants accepting contactless cards.

"It is fantastic that so many people are taking advantage of the ease and convenience of using their contactless payment cards to pay their bus fares," Shashi Verma, TFL's director of customer experience, said in a news release. "Each week we are setting a new record for usage, which gives us great confidence for when we launch contactless payments on the rest of the network and make contactless fully integrated in 2014."

TFL stresses the need for customer education when introducing a new ticketing system, and said it continues to remind customers about presenting their Oyster or contactless payment cards separately to buses' yellow card readers. If two cards are touched together, there is no risk of double payment, TFL said, but the payment might be taken from the card that the customer did not intend to use.

TFL said there have been no technical issues since its contactless payment system launched, and refund requests for charges made to the wrong card have averaged less than three per day, out of around 4 million daily bus journeys paid for on Oyster.

The company said it is working closely with the payments industry to prepare for the next phase of its contactless card rollout to trains. A pilot will take place over the next few months to test contactless payments on TFL’s train networks.

Learn more about contactless/NFC.