The NSW government will match the $42 million commitment for two new northbound and two new southbound climbing lanes on the M1 Princes Motorway between Bulli Tops and the Picton Road interchange.

The northbound climbing lanes are planned at locations between Cataract Creek and Bellambi Creek, while southbound lanes would be between Bulli Pass and Cataract Creek.

In its May budget, the Gillard government announced the climbing lanes would be built as part of the next phase of the government's Nation Building Program, with the extra lanes to be built between July 2014 and June 2018.

However, in October, the project appeared to suffer a major setback when the new Deputy Prime Minister and Infrastructure Minister Warren Truss said only projects with signed contracts would be honoured by the new federal government, with the climbing lanes project considered "an election commitment".

Despite this, the NSW government continued planning works to get the project "shovel ready".

Minister for the Illawarra John Ajaka and Heathcote MP Lee Evans welcomed the latest announcement of federal funding.

"These are projects the former federal Labor government promised to build but didn't fund," Mr Ajaka said.

Mr Evans said the upgrade would benefit the 35,000 vehicles that used the stretch of road every day.

In a joint statement, the two MPs said the "timing for construction of the Mount Ousley Road climbing lanes will now be determined as the project moves forward".

Cunningham MP Sharon Bird welcomed the funding but took issue with "the rewriting of history".

"This was not an election promise, these climbing lanes were funded in the May budget," Ms Bird said.

"After the election, there was an indication the Abbott government would not be honouring this project and we wrote to the Minister who said it was in 'a review stage'.

"I am very happy about the commitment, but I am not happy about attempts to rewrite history."