Canterbury Police are "frustrated" with the number of drivers crossing the centre line on a stretch of State Highway 1 in the region.
Over two hours on Waitangi Day, North Canterbury Highway Patrol issued 18 infringements for the offence on SH1 just north of the Hundalee mountain range, with each motorist receiving a $150 fine and 20 demerit points for failing to keep left.
"At least one of the motorists observed at one point had all four wheels of the car on the opposite side of the road, on a bend," police said in a statement this morning.
"It was disappointing to see so many motorists risking their lives and that of their passengers and other road users by crossing the centre line," Senior Constable Andy Palmer added.
"This is how head-on collisions occur.
"We intend to carry out more of these operations in the near future, to influence better driving behaviour on our roads."