It costs more than $60,000 a month to remove graffiti from Auckland motorways.
NZ Transport Agency acting system manager Wayne Oldfield said 123 tags were removed from motorway structures, fences, signs and gantries last month.
And that was low in terms of some months, when up to 350 are removed.
Oldfield said it costs $500-$2000 per site to clear graffiti, depending on labour and removal methods, but safe access to many places along the motorway network can vary from $1500 to $10,000.
"There is often interruption to the transport network when we remove graffiti.
"Often we try to schedule the removal activity to coincide with other works, however the highly reactive nature and desire to achieve rapid removal means we generate additional closures on the motorway at night."
Oldfield said vandals are putting themselves at risk when tagging on or near the city's motorways.
"These risks include falling from any of the structures, entering the restricted access motorway corridor, collision with vehicles, slipping down slopes and getting snagged or injured as a result of vandalising our structures," he said.
"Graffitists not only place themselves at risk, but also members of the public using the motorway. They may also drop items on the road posing a risk for motorists."
He said the types of graffiti also vary.
"Recently we noted the high level of 'tags', which are a rapidly applied, single colour and an apparent effort to cover a large area.
"This is in contrast to the more common piece or throw-up types of graffiti."
Oldfield said the agency recorded the tags and worked with Auckland Council in to identify and catch the vandals.The Summary Offences Act states that it is illegal to "damage or deface" any building or other structure by writing, drawing, painting, spraying or etching on it, or by marking it in some other way.
This offence also covers tagging roads, trees or other property like trains, cars and yachts.
Offenders can be fined up to $2000, or given a community-based sentence, or both.
Police may als lay intentional or wilful damage charges, which carry higher penalties.
It is also a criminal offence just to have spray cans or markers without a reasonable excuse or if someone could reasonably conclude they were going to be used for illegal tagging or graffiti.
Offenders can be sentenced to community work, or fined up to $500, or both.