Good wet-road skid resistance is vital to delivering a safe, well-performing road. This is why we operate a stringent skid-resistance measuring and maintenance programme. Skid resistance is affected when surfaces get polished by traffic or lose their texture through everyday wear and tear. To maintain surface performance, we apply strict limits to the type of chip that can be used on our highways, while balancing durability qualities with the costs of transporting chips from more remote locations.
We monitor all state highways so that we know if the skid resistance on any section has reached its minimum safety standard. We monitor some sections, such as rail and pedestrian crossings and tight curves, more carefully as they must maintain a high level of skid resistance.
Ways of improving skid resistance include:
water blasting to expose more of the stone chips
resurfacing the road using new chipseal or asphaltic concrete.
We measure a road's skid resistance using a Sideway-force Coefficient Routine Investigation Machine (SCRIM+).
This specialist vehicle is equipped with a range of information-gathering equipment and carries a weighted wheel that moves sideways to the line of travel. The wheel measures the resistance offered by the road surface to tell us how good the skid resistance is.
Every state highway in New Zealand is surveyed like this each year, using the same vehicle with which we collect other pavement and surfacing information.