The 80kmh limit was implemented in July last year and covers about 3.5km from the south boundary of Oamaru to just south of Alma.
The aim was to reduce accidents along that stretch of State Highway 1 and improve traffic safety after a petition and pressure from the local community, the Waitaki District Council and police.
However, some motorists are still exceeding the limit and highway patrol sergeant Peter Muldrew said the number of speeding infringement notices issued since the limit was introduced was much higher than before the limit was changed..
While there was "no set answer" to why motorists were not observing the limit, some reasons could be complacency, inattention or the semi-rural aspect of some of the 3.5km it covered, Sgt Muldrew said.
In recent times, those exceeding the limit were generally from outside the region, passing through Oamaru and Alma.
Heavy motor vehicles, particularly long-haul trucks, were also in that category.
Local people had improved over the past six months.
Common infringement speeds were in the 91kmh to 93kmh bracket.
The limit was well posted, with large green 80kmh speed signs at each end, and reminders in the middle of the stretch, Sgt Muldrew said.
The highway patrol monitored the area, particularly during heavy traffic volumes such as on Sundays.
Sgt Muldrew said the number and severity of crashes along that stretch had dropped since the new limit was introduced.
That included the overhead railway bridge at Alma, where double yellow lines had been painted, highlighting the need for people to keep left and making motorists more aware of the centre line.
"Those lines have made a huge difference to people crossing the centre line. There are hardly any now, compared to six months ago," he said.
