Motorists travelling through the Mackenzie Basin are being urged to slow down and drive with extreme caution, as black ice and freezing fog pose serious risks on South Island highways this week.

System Manager Mark Pinner said icy build-up is a major concern in sheltered areas along SH8.

“Bridge surfaces can cool quickly, and re-freezing can even occur in the late morning,” he said.

“We‘ve already had reports of people driving too fast for the conditions and truck and trailer units fishtailing. We also know it’s going to get busier later in the week as we get closer to the long holiday weekend for Matariki.”

Pinner said reducing speed is the most effective way to avoid crashes and keep roads open.

To help manage the risk, a Temporary Speed Limit of 50km/h has been introduced at several high-risk locations along SH8, including both sides of Lake Tekapo township, the Tekapo Military Camp, the Tekapo Flyover, and Simons Pass.

“This is not our usual approach, but the nature of the conditions forecast for this week means we need to use every tool we can to keep people safe on the roads,” he said.

He also warned that usual de-icing methods are becoming less effective in extreme cold, and while gritting continues, it is essential that motorists adjust their driving to match conditions.

“If the conditions warrant it, we will close the highway, most likely overnight and through the high-risk early morning period. People need to plan ahead if they are travelling in the area – keep an eye on our Journey Planner site.”