M2 motorway widening in Sydney's north-west is set to begin this year with the cost shouldered by the motorway's toll.

Hills Motorway, M2's operator, and the Australian Road and Traffic Authority (RTA) had inked a contract for the project today, which involves $550 million upgrade with four on and off ramps, and widening of the entire motorway to three lanes.

Tolls for the motorway will go up to $6 each way. Road Minister David Borger said motorists would continue to pay up to 2046. The period is four years longer than originally announced.

"Well people will only pay the one-off 7.7 per cent increase after works are actually completed so the increase won't actually kick in until people see a benefit for the increase," said Mr. Borger.

RTA said that no additional bus lanes will be made, as these are not part od the project. Work on the motorway will begin later this year in December.