The State Government is set to announce $4.6 million in Tuesday's state budget to investigate options for a new outer orbital motorway which could be built west of the city and provide a direct link between the Central Coast and the Illawarra.

Roads Minister Duncan Gay said the potential new M9 Outer Sydney Orbital could be built west of the M7, connecting the growth centres of Camden, Penrith and Windsor.

Map of the proposed motorway.

The budget, which the government says includes the largest roads package to be announced in Australian history, includes $4.6 million to continue strategic planning investigations for the motorway.

Mr Gay said the M9 was listed as one of 19 corridors identified for preservation in the 2012 Long Term Transport Master Plan.