Just 12 per cent of NSW voters believe the $16.8 billion WestConnex motorway project will be a bad outcome for Sydney once it is completed in three stages over the next eight years, an exclusive Fairfax Media poll shows.

While the construction of the new motorway has been highly controversial in Sydney's inner west, the poll of 1600 voters shows almost 48 per cent believe WestConnex will be good for the city. About 40 per cent of voters were undecided.

The results of the ReachTEL poll commissioned by Fairfax Media came as the state government confirmed that tolls will be reintroduced on a 7.5-kilometre section of the M4 in the first three months of next year following its widening as part of WestConnex.

Under the distance-based pricing for the project, motorists will be charged up to $4.21 for a one-way trip on that section of the M4.