The NSW coalition has pledged to duplicate 31 kilometres of the Great Western Highway between Katoomba and Lithgow over the next decade at a cost of $2.5 billion.

The government also pledged $960 million to upgrade further sections of the Princes Highway along the state’s south coast.

Deputy Premier John Barilaro and Bathurst MP Paul Toole on Wednesday announced construction would begin on the Great Western highway in the next term if its wins the March 23 election.

The project would be completed by 2028, the Nationals leader said in a statement.

The government will start with the construction of the Medlow Bath upgrade, the Mount Victoria bypass and works between Jenolan Caves Road and South Bowenfels.

Planning and design for other parts of the project will also begin in the next term, Mr Barilaro said.

Premier Gladys Berejiklian on Wednesday also announced a $960 million upgrade of the Princes Highway.

In its next term, the coalition plans to build the Moruya bypass and duplicate sections of the highway between Jervis Bay and Sussex Inlet, the premier said in a statement.

Planning work will also begin for the Milton and Ulladulla bypass as well as upgrades for the Princes Highway between Burrill Lake and Batemans Bay.

NRMA spokesman Peter Khoury said the funding commitment was a “welcomed announcement for a notorious highway”.