Drivers have racked up $500,000 in unpaid tolls in six months on the new northern toll road north of Auckland.
Figures have been issued by the Transport Agency for July - December last year.
The agency has called in debt collectors to go after the worst offenders.
One driver accrued more than $700 worth of unpaid tolls in the period.
From July, the agency says persistent toll avoiders will have a $40 fine added to every unpaid toll.
