Gold Coast commuters would get a new motorway to take pressure off the notoriously congested M1 if the Liberal National Party wins government.
Opposition leader Tim Nicholls has committed to splitting the cost with the federal government of a $500 million four-lane arterial between Nerang and Stapylton.
But Labor claims the former treasurer has got his numbers wrong, and the project would actually cost $2.4 billion.
"He's making up some of the facts, he doesn't have a business case, he doesn't know the cost," Premier Annastacia Palaszczuk said on Saturday.
Mr Nicholls said Prime Minister Malcolm Turnbull and federal Urban Infrastructure Minister Paul Fletcher were "very supportive" of the project, but he expects they would want to see the plans.
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He said the estimated $14 million per kilometre pricetag was based on the costings by the southeast Queensland regional council of mayors.
"We're confident that the numbers are right," Mr Nicholls said.
"Gold Coasters are sick of sitting in traffic day in, day out. Our plan for a second M1 will get people home from work sooner."
The proposed motorway is expected to run parallel to the existing M1, which is regularly clogged by accidents and peak-hour traffic.
Its construction would also support more than 1500 local jobs and take 60,000 vehicles off the M1, the LNP claims.
Mr Nicholls said the state government owned some of the land along the planned route, but property would have to be acquired from a "range" of people.
"We will be speaking to anyone who is an affected landholder," he said.
