What to dowhen striking black ice
Black ice has been in the news recently, most dramatically when a tour bus crashed east of Te Anau. So what is black ice, when is it likely to form, and what should drivers do about it?
According to that online font of information, Wikipedia, black ice is often incorrectly used to describe any type of ice that forms on roads, even when standing water turns to ice as the temperature falls below freezing.
‘‘Correctly defined, black ice is formed on relatively dry roads, rendering it invisible to drivers. Bridges and overpasses can be especially dangerous. Black ice forms first on bridges and overpasses because air can circulate both above and below the surface of the elevated roadway when the ambient temperature drops, causing the bridge pavement temperature to fall more rapidly.’’
It’s called black ice because it tends to look like the rest of the pavement on the road. Black ice forms without creating bubbles.
Transport Agency senior journey manager Neil Walker said black ice is commonest in shady areas and on bridges – early morning and late at night.
Drivers should take care in shaded areas caused by high banks and tall trees where roads freeze sooner and ice may not thaw during the day.
Bridges may also stay slippery for longer than other road surfaces, so slow down when crossing them. Frost is more severe at daybreak, so while it may not be frosty at 6am, it could be an hour or two later.
When there is a risk of black ice, drivers need to slow down and keep well behind other vehicles to reduce the risk of skidding.
If drivers hit a patch of black ice they shouldn’t brake. In shady spots and going across bridges, you should drive very carefully. When going across a bridge don’t brake, just keep the car going forward and keep the speed down.
If you’re going round a corner and it’s shady, definitely slow down.
An Otago Rescue Helicopter arrives as a passing bus stops to pick up some uninjured passengers from the recent bus crash on black ice east of Te Anau.