Police are defending using a $220 per hour airplane to spot dangerous drivers, despite only catching two drivers during the flight.
The plane was used for an hour and a half to spot dodgy driving between Blenheim and Nelson before Saturday's Super 12 rugby match.
The tactic led to twodrivers being fined $150 each for slow driving.
Traffic spotters in the plane had radio communication with four police cars ready to respond to reports of dangerous driving.
Tasman District Highway Patrol team leader Eric Davy defended the use of the plane, despite catching only two drivers for "impeding the flow of traffic".
Holding traffic up by not allowing it to pass was an offence police regarded as seriously as speeding, he said.
"It leads to people acting stupidly to get past them. They will overtake them when it's imprudent to do so, and that's why you have head-on crashes."
At $220 an hour, Mr Davy said it was hard to equate the cost of using the plane with the outcome.
"You've got to look at the amount of money we spend on road traffic enforcement in relation to how many lives we save, and this is just one tool of ours ... It's part of police presence and it's part of a whole strategy in reducing road trauma."
Mr Davy said the plane would be used again at Easter, although that would be the last time this financial year.
