What to dowhen striking black ice

Clutha Leader - - FRONT PAGE - STAFF REPORTER

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.

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