New Zealand's terrain and climate pose a number of challenges for our state highway network. Ranging from unstable hillsides to significant seasonal changes in surface temperature, such factors can result in damage to highways that can reduce the level of service they provide. An intensive monitoring and reporting regime helps us to ensure that problems such as blocked or washed out roads and melting or frozen road surfaces are responded to as quickly as possible.

Maintenance in emergencies

While we spend about $6 million a year on mitigating these risks, flooding, slips and crashes do happen. When they do, our contractors have to respond quickly to deal with blockages and update road information for drivers. We typically allow $50 million each year (or 10% of our total maintenance and operations budget) to respond to emergencies and restore service for our customers. 

We also provide Bailey bridges for a variety of events, including emergencies when existing bridges or other structures are washed out. These 'kit-set' bridges are versatile and relatively quick to construct and dismantle. Find out more about our Bailey bridge service.

Maintenance in tough climates

New Zealand's climate can also cause problems on the state highways.

In summer, surface temperatures can reach up 60 degrees celsius, requiring grit on melting road surfaces to prevent the road surface from being picked up by vehicle tyres.

In winter, we have to deal with widespread ice and snow. Our key weapon against ice on the roads is calcium magnesium acetate (CMA), sometimes mixed with grit. This substance lowers the temperature at which water on the road surface freezes. However, it's expensive, so we use it where it is most effective, based on local knowledge of hazard spots, and thermal mapping. This process uses data from strategically placed remote-reporting weather stations to predict where on the network icing is likely to occur. The prediction relies on the 'thermal map' we have built up of the network from sophisticated survey techniques. 

Find out more about our winter service requirements [PDF, 340 KB]. 

We also use remote-reporting weather stations for predicting the likelihood of avalanches. Our most hazardous route (State Highway 94 from Te Anau to Milford Sound(external link)) used to be closed for many weeks of the year because of harsh winter conditions. Now, our sophisticated avalanche management programme keeps the road open most of the time. In 2008, this programme won a major international award for maintenance management.