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Motorists on Auckland's new Northern Gateway toll road could face fines of up to $60 if they fail to pay their way within 28 days.

And although tolls will start at about $2 for cars and $4 for trucks and buses when the $365 million motorway extension between Orewa and Puhoi opens early next year, they will be at least duplicated if left unpaid for more than three days.

The Ministry of Transport has yet to determine the level of penalties for toll dodgers.

But Transport Agency (formerly Transit NZ) national toll project chief Brent Maguire said yesterday his organisation was seeking approval for an amount between $40 and $60, similar to penalties for upper-end parking offences, for those who fail to pay within 28 days.

He also disclosed that the agency was seeking between $4 and $5 to cover administration costs combined with unpaid tolls after three days.

"It won't be disproportionate to the value of the toll," he said.

The exact amounts of the new tolls, the first on State Highway One since those on the Auckland Harbour Bridge were abolished in 1984, have yet to be determined in line with latest inflation movements.

Mr Maguire said a major public information campaign would precede their introduction, to make all motorists aware in advance of the cost of using the new 7.5km road, to minimise infringements.

Prominent signs would offer those approaching the road the choice of turning off SH1 to the free alternative route along the Hibiscus Coast Highway. Those choosing to save time and fuel in return for a toll would be encouraged to pay beforehand, by one of several ways.

The easiest for frequent travellers would be to set up an account for automatic deductions, although one-off payments could be made by phone, on the internet, or at cash machines at each end of the road.

One cashpoint would be at the BP Connect service centre south of the toll road, and the other near Puhoi at the northern end. But Mr Maguire said casual users who did not make preliminary arrangements would be given three days' grace to pay up, before incurring administration fees.

The electronic toll system is designed to keep traffic flowing freely, at speeds up to the 100km/h open road limit, without any need to change lanes or stop.

Cameras and infrared lights have been installed on three overhead gantries near the Orewa end of the road to capture number-plate images of every vehicle passing below, from front and rear, no matter its speed.

Each vehicle will be allocated a unique identifying number, and the images fed into banks of computers stationed next to the 6m gantries.

Mr Maguire said the roadside computers would hold information about all payments made, and store the images for three days without any further action.

Images of any vehicles on which tolls remained unpaid after that time would be copied to the national transport registry centre in Palmerston North, so their owners could be identified and notices sent to them.

He said the toll collection equipment was of the third generation of technology being used in about 40 countries, and had proved to be highly accurate.