Toll road authorities are chasing more than 38,000 unpaid fees.

Figures released by the Transport Agency show that in four months since the Northern Gateway Toll Rd opened 38,253 trips have not been paid for.

But that is only a tiny fraction of the more than 1.5 million chargeable trips on the road to the end of May.

The Transport Agency said that meant 93.5 per cent of trips were paid for, which it put down to drivers becoming more familiar with the payment options since the road's controversial opening.

The agency was forced to hire on-site "ambassadors" to help people use the pay stations, but it said yesterday they were no longer needed.

Since the 7.5km motorway extension opened on January 25, more than 100,000 toll payment notices have been issued for trips that are not paid for within three days.

Motorists who fail to pay within three days face an "administration fee" of $2.20 in addition to any unpaid toll.

Those who ignore reminder notices for more than 28 days face an extra infringement fee of $40, and risk being taken to court if they do not pay within a further 28 days.

The cost of pursuing these unpaid tolls has not yet been calculated, and the agency has not decided whether to refer the unpaid amounts to a debt collection agency.

Just 0.39 per cent of all the trips have managed to get through the automatic cameras and manual checks without being recorded.

The agency said about a quarter of all motorists using the route still took the free option through Orewa and Waiwera.

Meanwhile, agency figures show fewer than 50 per cent of motorists used a prepaid account.

Half of the remainder used a kiosk to pay the toll, with half of those using a credit card.

Although, at the moment, motorists can pay online or by phone, using only Visa or Mastercard, the Transport Agency is looking at expanding the range of acceptable credit cards.

Trips recorded during first four months of operation.

Trips not paid within three days.

Trips still not paid for.

Cost for a car to travel on the toll road.

Cost for a truck.

$2.20Extra cost if you don't pay within three days.

Extra cost if you don't pay in 28 days.

0.39 per cent
Vehicles who escape identification during their trip.

27 per cent
Motorists who use the free route.