ACT secretary Klaus Pinkas said the Liberals' proposal, unveiled on Thursday, had "some good ideas and great lines on the map", but was uncosted. He said bus drivers supported the idea of fewer stops on express services.

"I can't fault where they're running buses," he said. "It all makes sense and it looks good.

"But it's just not costed. I don't know, you don't know and [Liberal leader] Jeremy Hanson doesn't know what the cost is."

A Liberal government would increase the number of direct, rapid routes from two to eight, allowing people to travel directly from Tuggeranong and other centres to the city with few stops.

The plan would see buses run till 1am three days a week and run ACTION as a seven-day service rather than separate weekday and weekend services. The Liberals would offer free travel after the first eight trips each week, and promise no current bus stop will be closed.

The Liberals believe they can deliver the plan for the same amount currently spent on ACTION and the Capital Metro Agency combined, about $160 million a year. But the party admits it has no firm costings.

The government dismissed the proposal as "massively undercosted", but did not provide any of its own figures on what the Liberals' proposal might cost.

Mr Pinkas said Labor's plan for a tram line to Gungahlin was better because it meant far more jobs in construction. He said the Liberals' proposal would mean more bus drivers, but Labor's project would bring hundreds of construction jobs to build the tram and redevelop Northbourne Avenue.

"There's swings and roundabouts on the Labor proposal and the big gain is the jobs in the redevelopment of Northbourne Avenue," he said

"Capital Metro's not just about the trams. It's not just about moving the good burghurs of Gungahlin into the city and back again. It's about the redevelopment of Northbourne Avenue... that's what's attractive to TWU members across the construction industry."

The Liberals also propose a rapid service to Canberra Airport, plugging a long-lamented gap in bus routes. But it is unclear whether such a route could be delivered, given the current impasse, with the government so far unable to persuade the airport to allow ACTION buses.

A spokeswoman said the airport "welcomes any discussion about ground transport to the airport" but pointed out there were already ACTION buses to the Brindabella Business Park, about 500 metres from the terminal. A privately contracted shuttle bus ran from the terminal to Russell and the city.

Transport Minister Meegan Fitzharris said the Liberals' proposal would cost hundreds of millions and take years to implement.

She said the policy lacked costings and relied on the Liberals spending millions on compensation to tear up light rail contracts. The government plans to create new bus routes after 2019, including through redeployment of buses from the city to Gungahlin corridor as tram services begin. They could include services to the Molonglo Valley and Weston Creek.

Ms Fitzharris said hundreds of new buses would be required for the Liberal plan, as well as at least two new depots. She said dead running would be an inevitable result of route specific vehicles and she questioned idea of colour coding buses.

"Labor introduced rapid bus routes, so we are obviously committed to those and we will be making further announcements with the roll out of our integrated transport agency on July 1 and also further announcements as we get closer to the election.

"I think there is no detail in the Canberra Liberals' plan. I think it is massively undercosted and I think we will be challenging them to provide actual costings for this, of what it will cost on top of the costs they will need to pay for scrapping and tearing up the light rail line."

A community survey about ACTION services is planned in April and Ms Fitzharris said it would help guide improvements to bus services.