"I knew exactly what they were up to but couldn't do much."
He said the students were directly above him when the stone was dropped, striking his windscreen. Luckily it did not shatter the screen but caused a crack.
Mr Campbell said he maintained control of the truck and stopped at Springs Flats where he phoned *555 and urged police to get to the scene as soon as possible. He continued on his way north.
"The police needed to get there and give the kids a rev up. These kids just don't understand how this can go wrong. How would they feel it they'd thrown that rock and it took out one of their family members coming the other way?"
Mr Campbell said several other truckies said they had experienced similar incidents at the same bridge and he said a camera might need to be installed.
Whangarei police Senior Sergeant John Fagan said officers went to the bridge on Monday but the students were no longer there. An officer was at the school the students were believed to be from yesterday continuing to investigate.
"This is highly dangerous activity with the potential to cause serious injury or kill someone if a rock hits the vehicle below," Mr Fagan said.
"Motorists just aren't expecting a rock and at the end of the day it could be life threatening."
Mr Fagan said if people spotted people acting suspiciously on or near the bridge they should contact police immediately.
In August 2005 Christopher Wayne Currie, a 20-year-old apprentice in the building trades, died after a stone was deliberately thrown at his car as he drove along a motorway near Auckland.
Ngatai Rewiti, who was 14 at the time of the incident was found not guilty of Mr Currie's murder, but guilty of manslaughter in 2006.
