The government's roading agency says it has successfully prosecuted a driver who owed more than $5000 in unpaid tolls on Auckland's Northern Gateway.

Robert Masaberg, from Snells Beach, did not appear but was convicted in North Shore District Court on Tuesday of 20 charges of failing to pay a toll, the New Zealand Transport Agency (NZTA) says.

He was ordered to pay $1157 in fines, court and prosecution costs.

At the end of October, Masaberg owed $5181 in unpaid tolls, administration fees and costs racked up since the $372-million toll road was opened four years ago.

However, the NZTA says it hasn't finished trying to get the money out of Masaberg and will assess the impact of the prosecution before deciding on its next move.

NZTA's Celia Patrick says the 20 charges send a clear message to toll evaders.

"Their behaviour is unacceptable to the vast majority of drivers who pay their tolls on time."

NZTA now plans to prosecute three other people, who allegedly owe $3780, $900 and $500 respectively.

Since NZTA began its prosecution process, there has been an increase in the number of people paying tolls before a five-day period expires.

About 96.5 per cent of drivers pay on time, but NZTA is still owed $238,000 in unpaid tolls and fees for the first three months of the financial year.