The country's first weather-activated speed limit signs will kick into action this week, targeting motorists travelling between Waikato and the Bay of Plenty.
Twenty-two new signs on a 12km stretch of State Highway 29 over the Kaimai Range will go live at 9am today.
The signs, and four web cameras, will be linked to a weather station at the range's summit and the New Zealand Transport Agency will then be able to adjust the speed limit between 30km/h to 100km/h, depending on conditions.
Police will be enforcing the variable limit.
NZTA chief safety adviser Colin Brodie says the two-year trial aims to encourage people to drive at safe speeds in rain, ice and fog.
Despite changeable weather people still tried to travel over the range at 100km/h, he said.
More than 70 percent of Kaimai crashes happened in wet weather and more than 40 percent of those were because of drivers going too fast.
The signs will allow NZTA to drop the speed limit to 60km/h on the Waikato side and 80km/h on the Bay of Plenty side.
The limit could be reduced to as low as 30km/h in the case of a crash or road works.
If the trial is successful, and there is a reduction in death and serious injuries, the system may be introduced across similar sites around New Zealand.