Two cars belonging to one person have made almost 700 trips on the Northern Gateway motorway without paying the $2-a-trip toll - and the owner now faces fines of more than $26,000 if the fees are not paid.

Other repeat toll dodgers are also being lined up for thousands of dollars of fines.

The Transport Agency, which is preparing to take court action against non-payers, says the worst offender owns two cars which have made 667 unpaid trips along the 7km road between Orewa and Puhoi since it opened in January last year.

That person owes $1879.20 in arrears - at $2 a trip plus administration costs - and could become liable for infringement fees of more than $26,500 unless the arrears are cleared within a fortnight.

Transport Agency regional director Wayne McDonald said letters were being sent this week to the worst toll evaders telling them to pay up or face a $40 fine for each outstanding trip.

"For offenders with several hundred unpaid trips, this will mean fines totalling tens of thousands of dollars if they do not pay their debts," he said yesterday. An agency report listed 55,964 vehicles which had racked up unpaid tolls and administrative fees of $525,254 over the toll-road's first 11 months of operation.

That was just over 5 per cent of total revenue of $9.84 million. Owners of 15 vehicles owed more than $300 each.

Debt collectors have started chasing dodgers, but the report said the Transport Agency had held off until now from issuing infringement notices in favour of a "phased approach" to recovering fees.

This had been done because compliance toll rules were already good and the agency wanted to give motorists time to become familiar with the road's electronic toll collection.

An administration fee of $2.20 is charged on tolls unpaid for more than five days, although a single fee can cover several trips if these are made on the same day.

Trucks are charged $4 a trip and motorcyclists will face a $2 toll from today after enjoying free use of the road since it opened.

Toll opponent Hans Grueber, who lives inland from Waiwera, said that although he did not use the road often, he was the registered owner of a car which had made several unpaid trips.

He would welcome being pursued for arrears so he could argue in court that tolls were introduced illegally.

The Transport Agency report says 4.3 million journeys have been made on the road - 76.5 per cent of traffic movements between Orewa and Puhoi, against a target of 70 per cent.

The rest of the traffic uses the free coastal Hibiscus Highway.

In the the six months to December, the extra traffic volume enabled the agency to repay $2.9 million - 4 per cent more than expected - of a 35-year loan of $159 million towards construction of the $356 million road.

But the toll collection cost of 78c a transaction is still more than a Government-imposed limit of 65c, so the agency is covering the difference from a $3.3 million "residual project" fund set up when the road was completed under budget.