Ahead of schedule: the Opal card system is being rolled out at select train stations.

Ahead of schedule: the Opal card system is being extended to select train stations. Photo: Dallas Kilponen

About half of all Sydney train passengers will be able to use Opal cards by the end of next week.

Transport Minister Gladys Berejiklian said on Thursday that the distribution of the public transport smartcard system is ahead of schedule.

But at 2.50pm, the Opal website, which allows people to buy a card, was overloaded and could not be used.

Website crashed: opal.com.au is down.

Website crashed: opal.com.au is down.

From Friday, January 31, the Opal will be available at train stations between Strathfield and Redfern, Strathfield and Hornsby, Chatswood and Wyong, and on the Epping to Chatswood line.

Announcing the latest stage of the $1.2 billion ticketing system at Strathfield Station, Premier Barry O'Farrell and Ms Berejiklian said the government was on track to ensure the card could be used on all trains, buses and ferries by the end of the year. The light rail will be added next year.

"We are slightly ahead of schedule," Ms Berejiklian said, "but I say that without being complacent.

"If you look at the way other cities around the world and around Australia have implemented integrated ticketing, it hasn't gone without problems. It hasn't gone without glitches," she said.

"Even though we've had great success to date, we will never be complacent."

The Opal is already available on the eastern suburbs line to Bondi Junction, on the city circle line and on the north shore line to Chatswood, all Sydney Ferries, and two bus routes.

But the take-up of the card has been fairly slow. Some public transport users have been put off by the relative cost of paying with the card, which can be more expensive than using a monthly or quarterly ticket.

Others have been waiting for it to be extended to more train stations and buses.

Ms Berejiklian said the additions of the stations next week would be the biggest test of the system so far.

She said the extension to other train lines in Sydney – for instance, the western line to Penrith and the Blue Mountains, the Bankstown line or the Campbelltown and East Hills line – would depend on the success of the extension.

To make the Opal more attractive, the government froze fares on Opal when it increased them on paper-based tickets this year.

That means that commuters in western Sydney who do not have access to Opal cards yet are paying relatively more than inner-Sydney commuters who can use Opal.

Ms Berejiklian said she wanted to encourage commuters to use the Opal.

"Under Opal now you have the potential to save more money," she said. "It was a conscious decision on the part of the government to freeze Opal fares while paper ticket fares went up in accordance with the cost of living."

Under the Opal fare structure, once a commuter has paid for eight "journeys", they travel free for the rest of the week. But one journey might involve multiple trips: for instance, a bus trip to a train station, followed by a train trip would count as one journey.

Experts have criticised the decision to continue to charge people different fares when they change from one mode of transport to another. But Ms Berejiklian said she did not think users of different types of transport should subsidise the other.

"We don't think it's fair that people who catch trains and buses should be subsidising people who catch ferries," she said.

"Every mode of transport costs a different amount for the government to provide, and we want to make sure it's an open and fair system."

About 45,000 Opal cards have been registered, and the government has not yet said when it will stop selling paper tickets.

Mr O'Farrell said queuing for a ticket would be a thing of the past. "This is particularly great news for customers on the central coast," he said.