How to drive safely in icy, wintry conditions

With the country marking Road Safety Week, road users are advised to take extra care when driving on icy roads in wintry conditions.

In July 2024, two tour buses travelling along State Highway 8 between Tekapo and Twizel in the South Island overturned in treacherous conditions within a few hundred metres of each other. Fifteen people were rushed to hospital, with two seriously injured.

Locals blamed a winter phenomenon known as "black ice" for the crashes.

And yet black ice is far from the only thing to be mindful of when driving in difficult conditions.

What follows is a quick reminder of a few things to pay extra attention to when driving in winter months.

Isn't the road toll going down?

According to the latest data compiled by ACC, total road accident-related compensation claims reached nearly $750 million in 2024, with more than 50 percent involving driving accidents.

Meanwhile, latest data compiled by the New Zealand Transport Association shows 292 people died in 250 fatal crashes recorded nationwide in 2024.

While the total death toll is a slight improvement on the figures recorded in 2023, police say there is always room to reduce the number of casualties on the road each year.

Should I drive if my windscreen is covered in ice?

Many accidents in winter are caused by poor visibility after ice forms on windscreens in low temperatures.

Once ice has formed on your windscreen before you start driving, do not try to remove it with your window wipers.

This not only risks damaging the rubber on the blades, but it can also worsen visibility, as scraping the ice may blur your view.

Instead, use an ice scraper or a hard plastic card like a credit card to remove the ice before starting the engine.

If the engine has already been running for a while and the internal temperature of the vehicle is close to normal, drivers are advised to turn on the windshield's defrost function and let warm air melt the ice before then using wipers to clear the view.

It's worth noting that there are quicker but riskier methods that experts say should be avoided.

It's recommended that drivers refrain from pouring hot water onto a windscreen to remove ice.

If the water is too hot - making the windscreen's temperature difference with the outside air temperature too great - the glass can crack.

What should I do if I encounter fog?

In certain areas of New Zealand, sudden patches of dense fog can appear in colder months.

Drivers are first advised to turn on their fog lights, which are designed to penetrate thick clouds that form in such conditions.

Drivers of vehicles without fog lights should use their headlights on a low beam setting that is focused on the road immediately ahead.

In foggy weather, the moisture in the air scatters headlights on a high beam setting, which can impair visibility rather than improve it.

Additionally, drivers should slow down when driving in poor visibility, increasing their following distances and avoiding frequent lane changes.

What should I do if I encounter black ice?

Black ice isn't black - it's a transparent layer of ice that typically forms on a road after light rain or fog at zero degrees.

Because the transparent nature of the ice makes the road surface appear visible, drivers can mistakenly think road conditions are safer than they are.

Vehicles traveling on such surfaces often lose tire traction when changing direction, causing drivers to lose control of the vehicle.

Mark Revill-Johnson, chair of the nonprofit New Zealand Institute of Driver Educators, told Morning Report after the bus crashes in July 2024 that drivers could lose control of vehicles travelling at just 10 kilometres per hour, especially in foggy conditions.

"You should always be able to stop in the amount of road you can see and be able to do that on the correct side of the road," he said.

"So, if there's fog around, you can't 'out-drive' your view because you're not going to see stuff that matters."

AA recommends drivers should maintain a following distance that is 10 times greater than usual when driving on icy or snowy roads.

If you unintentionally hit a stretch of road with black ice, it's important to remain calm.

In such situations, AA advises drivers to refrain from trying to change direction suddenly.

Instead, continue travelling in the same direction, take your foot off the accelerator and avoid slamming on the brakes.

Braking hard can throw the vehicle off balance and make it harder to regain control.

For manual transmission vehicles, downshifting can help to reduce speed, if necessary, but any sudden movements that may destabilize the vehicle should be avoided.

Do I need snow tyres?

Compared to regular tyres, softer snow tyres offer better grip and improved driving safety in icy or snowy road conditions.

However, NZTA says snow tyres are not needed in most parts of New Zealand.

Snow tyres are only recommended for a very small number of people living in the southern regions of the South Island or those who frequently drive in alpine environments.

NZTA says all-season tyres are a better choice for most people.

Additionally, NZTA says that snow tyres should not be mixed with other types of tyres.

Are snow chains useful?

Anyone driving in extreme wintry conditions on unpaved mountainous roads should consider wrapping snow chains around tyres to improve traction.

Fans of skiing and other winter sports enthusiasts sometimes need chains in case of heavy snowfalls while ascending and descending mountains.

NZTA enforces snow chain regulations on specific alpine roads, particularly in the South Island. For example, Arthur's Pass and Lindis Pass often have mandatory chain requirements when snow or ice is present.

If you are driving in unfamiliar areas, NZTA recommends drivers to use its Journey Planner tool app, which offers real-time road condition updates and travel advisories to help them plan a safe trip.