In typical winters, grit spreaders covering the region's state highways had to deal mostly with white frost, which was visible.
But this year there had been much black ice.
Central Otago and northern Southland had been particularly badly affected.
Some days in Central Otago the temperature had not risen above 2degC and the pavement temperature had been as low as -11degC, he said.
On State Highway 85, the Pigroot, there had been an instance where drizzle was freezing as soon as it hit the road.
There had been quite a few road crashes related to black ice and the agency would be analysing those to see if there were ways of improving conditions on those roads to prevent such accidents.
In the long term, it was hoped that research being done on weather prediction in the United Kingdom could lead to more efficient ways of using grit and de-icing chemicals.
Fulton Hogan regional manager Richard Fulton, whose company grits Dunedin City Council roads, said one of the challenges for those spreading grit was that the distribution of frost and ice over the city could be extremely variable.
Inspectors went out about 4am to see where grit should go, but faced a changing situation.
People often did not realise that areas which were clear could later freeze, something which happened very quickly.
"You could stand on the side of the road at daybreak and watch it freeze within minutes."
City council senior contracts supervisor Peter Hughes said at this stage it was not possible to compare the amount of grit used this year with last year.
From July 5 to 16, there was only one night in Dunedin when grit was not spread, with more than 200 tonnes distributed on Wednesday, July 8, followed by Monday, July 13 (about 88 tonnes), and Tuesday, July 14 (120 tonnes).
Most of the grit went on urban rather than rural roads within the city boundaries.
