The next set of features on Transport for London's Oyster smartcard are soon to be launched in the next stage of its phased roll out.

Oyster Pre-pay, which allows passengers to pay for travel in advance, has already been introduced on the tube and Docklands Light Railway.

Its introduction on buses and trams is expected to follow within the next three months, later than scheduled.

Charles Monheim, Oyster's director of ticketing systems and fare policy, told vnunet.com earlier this year that "pre-pay will be rolled out on buses and trams in March 2004".

TranSys, the private consortium responsible for Oyster operations, declined to say why pre-pay on buses and trams has been delayed, and would not give a deadline for the introduction of 'capping' on the smartcards.

Capping is intended to ensure that customers are not charged for multiple single journeys across the network where a travel card rate would be cheaper.

Until then, Oyster pre-pay users who want a travel card will be forced to buy paper tickets.

This is because pre-pay needs to be fully operational across the capital's transport network for capping to be effective.

"The approach we have taken [to the introduction of Oyster] is low risk," said Steve Beer, chief operational officer at TranSys.

"We could have switched on all the features at once, but thought it far better to opt for new functionality a bit at a time."

Colin Penn, technical programme manager at TranSys, echoed the latest update from Transport for London representatives.

"We can confirm that capping and full pre-pay will be available sometime in the second quarter of 2004," he said. "We are in the initial phases of testing in garages and on buses and trams."

Transport for London and TranSys also announced that they are looking at integrating the rail network into the Oyster scheme, but would not say when this might happen.