If someone forgets to tap off, they will be charged the maximum fare for that bus route. Tap off or it'll cost you: Transport Minister Gladys Berejiklian. Credit:Dean Sewell Announcing the bus trial on Thursday morning, Transport Minister Gladys Berejiklian also said that commuters who change from one bus to another will not have to pay a separate fare under the new Opal card. But people changing from bus to train or bus to ferry will continue to have to pay multiple fares. Under the Opal, single fares will be slightly cheaper than current single MyBus fares and the three "MyBus" bands will be retained. But occasional bus users who use TravelTens will have to pay more under the Opal card, because the card does not have a "TravelTen" option.

For instance, the current adult MyBus 1 single fare is $2.20. Under the Opal the single fare will be $2.10. But anyone using a TravelTen currently pays $1.76 a trip, with the pass costing $17.60. An Opal card being used on the Neutral Bay to Circular Quay ferry service. Credit:Peter Rae The main price incentive offered under the Opal is that anyone who takes more than eight public transport trips a week travels free after the eighth. Occasional users, however, will not get the benefit of that. About a quarter of the 1.3 million bus trips made on an average weekday in Sydney are paid for by TravelTen. The fare structure for the Opal Card, which is already in place on all ferries and some train lines and which will be across most public transport by the end of 2014, will also encourage commuters to change from bus to bus.

Anyone transferring from one bus to another within an hour will pay just the one fare, measured on the total length of the trip. But the free "transfers" between buses will not extend to trains or ferries. For instance, the fastest way to travel from Bondi Beach to Town Hall in peak hour is to catch a bus to Bondi Junction Station and then change to a train. Under the Opal system, anyone doing this will continue to have to pay two fares. "We believe that customers should pay for the mode they are using," Ms Berejiklian said.

"We don't think it's fair that train and bus customers should subsidise ferry customers, for example. There are many systems around the world, some do it the way we do it, others have chosen to have a flat fare for every single mode. But we don't think that's fair." Commuters can still buy TravelTens and other multiple journey tickets like MyMulti and MyWeekly tickets.

On TravelTens, Ms Berejiklian said: “Opal fares are also cheaper than TravelTen tickets if you travel twice a day, Monday to Friday which is what regular users do. “The other big advantage of Opal is that you never again have to worry about ticket queues or which ticket to buy,’’ she said. The Minister said the government had not determined what fare structure would apply on light rail under the Opal card. The contract for the Opal card was signed under the former Labor government in 2010, and is worth about $1.2 billion.

It is currently in place on train stations in the City Circle, on the Eastern Suburbs Line, and on the North Shore Line to Chatswood. Ms Berejiklian said she expected some "glitches" as the card was extended to buses, due to the spread of infrastructure required. "It will be the most complicated part of the network, in terms of rolling it out," she said. "Five thousand buses means two readers on each bus, up to ten thousand readers – you need to make sure the equipment is not going to let you down at any stage," she said. The minister said the next bus route to trial the Opal would probably be an inner-city service run by the government-owned State Transit. The 594 is run by Transdev.

About 24,000 Opal cards have been issued to date. People using the Opal card have the option of loading money onto it automatically or manually. If an Opal is set to ''auto top-up'', and linked to a credit or debit card, the Opal will automatically reload with a set amount of money once its credit falls below a nominated amount. Commuters can also choose to add credit to their Opal cards at convenience stores, newsagents and shopping centres, using cash, EFTPOS or credit card.