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Traffic jams were not the only challenge facing the Transport Agency on the first day of Auckland's new $365 million Northern Gateway toll road between Orewa and Puhoi.

As motorists stewed in a very scenic gridlock, offering spectacular views of the Hauraki Gulf over regenerating kauri forest, electronic faults struck three of the four cash payment machines.

The malfunction was not critical, because of a sudden decision by the agency and Transport Minister Steven Joyce on Friday to declare the first two days of the road toll-free.

But it hardly inspired confidence among motorists who, after being stuck for more than an hour on the new road, decided to double back to Auckland from south of Puhoi at a turning bay which had both of its cash machines out of action.

One was not accepting cash, and the other not offering change for tolls of $2 for each one-way car trip after tonight, and $4 for vehicles over 3.5 tonnes.

Another machine, one of two on the southern approach to the new road at the BP service centre off the Northern Motorway at Dairy Flat, was also under repair.

Although the Transport Agency is confident of fixing all the machines in time for tomorrow, regional director Wayne McDonald played down their failure as incidental to the successful operation of the new road.

He used it to reiterate a message that motorists do not have to stop at the kiosks, as they will have 72 hours to pay tolls before incurring a $2.20 "administration" fee.

"It wouldn't have mattered if all of them were out, and we would have put them out anyway had the queues got too long," he said.

"People could have driven through - they would have been tolled and would have been sent a bill, so the system wouldn't have failed."

Mr McDonald said it was not unusual for new electronic equipment to fail.

Despite yesterday's traffic jams, he also remained buoyant about the long-term success of the new road.

Some motorists, although pleased with the engineering along most of its 7.5km route, were disappointed to find its two northbound lanes funnelled into a single lane on the 537m viaduct across the Waiwera River, just before the motorway disappears into one of two tunnels through Johnstone's Hill.

Although the tunnels are both 12m wide, the southbound version has two lanes and both have enough room for three.

But Mr McDonald said that until the motorway was extended further north, it would be too dangerous to allow two lanes through the northbound tunnel so close to the road's merger with the old coastal highway.