Gold Coast commuters would get a new motorway alongside 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.

Opposition leader Tim Nicholls on the Gold Coast on Saturday. Credit:AAP

"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," Mr Nicholls said on Saturday.

But Main Roads minister Mark Bailey said Mr Nicholls had made a major costing blunder, with the project actually expected to cost $2.4 billion.