Commuters have been left disappointed by the axing of free Opal trips, but transport experts have welcomed the $2 rebate for travellers using more than one public transport mode.

Transport Minister Andrew Constance announced on Wednesday that commuters who catch two forms of public transport within an hour, such as a bus and a train, will pay $2 less for their second trip from September. Concession, youth, pensioner and senior Opal card holders will pay $1 less.

Under Sydney's existing fare system, people are charged multiple times for changing between modes of transport.

Corinne Mulley, chair in public transport at the Institute of Transport and Logistics Studies at the University of Sydney, said the penalty for changing modes hindered an efficient transport system.

"Once you get people around to thinking about interchange, you can do so much more with your public transport system," Professor Mulley said."Two dollars is significant and it goes quite a long ways towards helping with the interchange penalty," she said.

The director of transport and cities at the Grattan Institute, Marion Terrill, said for some people the rebate would "tip them over to make public transport a viable choice".

"In many ways it is a historical accident, what combination of train and bus is available to people," Ms Terrill said.

But Ms Terrill said it was a shame the government had not adopted a recommendation to change the gap between peak and off-peak fares."It would be a really valuable contribution to managing congestion if the fare structure encouraged people who can to travel off peak," she said

But Sydney commuters seemed most concerned that they would no longer get free trips after making eight journeys in a week. Instead, they will now pay half price after their first eight.

"Now I'll have to think about where I travel after the eight, whereas at the moment after the eight I know I can travel anywhere I want for free," said Jay Gill, a commuter on Sydney's light rail line.

"In that respect I will probably use public transport a bit less. I'm not sure it's the best idea in the world, actually."

While the idea of cutting free trips had been floated since December, when a draft report into the Opal fare structure was released by the state's pricing regulator, commuters seemed surprised that the government had backed the idea.

Ailing Tay, who usually catches the train from Chatswood to Town Hall, said she was concerned her weekly expenditure would rise and she would now be less likely to catch public transport outside of her daily commute.

"For me, when I get my free trips at the end of the week, I go around places to explore, so without that there isn't really much of an incentive," Ms Tay said.

"I think the free trips after eight are great because it just means that people actually want to use the public transport, around that time you're not commuting so it's really sort of opening up a lot of areas," Chris Wall, of Woolloomooloo, said.

In this respect, public transport users have been doing only what the government encouraged: working out ways to get bang for their travelling buck.

"For me, it's going to be more expensive probably, because I don't swap modes at all – and then for Fridays I will have to pay, and for weekends as well," commuter Sarah McColl said.

Mr Constance's decision to reject the regulator's proposal to increase the daily fare cap for Gold Opal card holders from $2.50 to $3.60 was welcomed by seniors and pensioners.

"I think that's a good thing," said pensioner Peter Brownson.

"I think pensioners need to be able to get around and if it's cheaper for them to do so, all the better," said Mr Brownson, who was commuting on the light rail to Central.

"It's good for the older people, especially, who can't get around and don't have their own transport."