A $577 million contract to build a 1.7-kilometre light rail extension has confirmed the Canberra Liberals' "worst fears", showing the project was vastly more expensive than the opposition had thought the "white elephant" would cost.
Mark Parton, the opposition's transport spokesman, said the true cost of light rail stage 2A - which is planned to connect the city with Commonwealth Park - would be more than $800 million when the enabling works were included.
"What we're talking about here is that stage 2A has come in at more than double what the Canberra Liberals estimated. And when we look to stage 2 in its entirety, it's highly likely that we'll have a figure north of $4 billion," Mr Parton said.
"Now, I think we're talking craziness. I really do."
Mr Parton said it was optimistic to expect the Commonwealth would contribute half of the total project cost and to believe the first light rail passengers would alight at Woden before 2034.
Patience with the project would wear thin in the community, he said.
"The delays are extraordinary. I think we were working out in the office this morning that stage 1 moved from Gungahlin to Civic at about 22 metres a day. Stage 2A is going to move at about 1.5 metres per day," he said.
Mr Parton said it was a foregone conclusion that the extension to Commonwealth Park would be built, but stressed the Liberals' opposition to a further link to Woden.
"We're certainly not going to be in the business of tearing up contracts, so it's always been the Liberals' position that ... it was highly likely that we would end up at Commonwealth Park," he said.
Mr Parton said it would be a dereliction of his duty as a member of the Assembly to sign up to the "reckless" amount of money required to build light rail to Woden.
"It's astronomical. The government will have to borrow it at a time when obviously interest rates will be continuing to rise and it doesn't make economic sense to proceed," he said.
"And I think the government actually knows that because otherwise we wouldn't be staring down the barrel at arrival in Woden by - I mean, when will it be? 2034? Will it be 2040? Who knows."
The light rail extension to Commonwealth Park is still more than four years away from taking passengers, with the new timeline revealed after the ACT signed a $577 million contract for the project.
Construction will start from late-2024 and is expected to take about three years, meaning the 1.7-kilometre extension will open in January 2028, more than 8.5 years after the first stage opened between Gungahlin and the city.
The ACT government on Thursday announced it had signed the contract for the extension from the Alinga Street terminus to Commonwealth Park.
The federal government has contributed an additional $125.5 million.