Prime Minister Tony Abbott has announced $2.9 billion in new roads spending over the next eight years to support the construction of a new airport at Badgerys Creek, with NSW pitching in 20 per cent of the cost.

The announcement follows from Mr Abbott confirming yesterday that the Coalition cabinet had signed off on building the much-debated airport at the site 50 kilometres west of Sydney's CBD.

Construction of the airport is expected to begin in 2016 and will spur the creation of up to 4000 construction jobs at its peak.

NSW Premier Barry O'Farrell was expected to appear with Mr Abbott, but pulled out and then announced he was resigning as premier over revelations at the Independent Commission against Corruption.