Two buses in a three-coach convoy rolled within a hundred metres of each other along State Highway 8's Tekapo-Twizel Highway shortly after 8.30am on Thursday. Fifteen people were rushed to hospital, two seriously injured.
Other drivers on the road say conditions were treacherous and the highway should have been closed.
Tony McClelland was driving south to Omarama on State Highway 8 and called police after his van hit black ice.
"I just said, 'You guys have got to close this road - I almost just lost the van, almost ended up down the ditch, and next thing out of the fog coming towards me are these two white buses. No signage on the coaches.
"And they were flying."
He drove this stretch of road several times a month, and said the conditions were the worst he had ever seen, and there were not enough warnings.
"There's only a sign up by the airfield, the Mount Cook airfield on the left hand side as you're heading south, just saying 'winter conditions, caution - black ice' or something along those lines. Some people - it's not big, mate - people can't read that in fog. It's just got me mindblown, really. Should have been closed."
Grace, a traveller from Australia, was driving north and pulled up to help injured passengers.
"We immediately jump out and start providing first aid to the people, and they don't speak much English - however, the ones that do can let us know that the bus just slipped.
"There was no fatalities, thank god, but the children were quite lacerated from the glass, I believe. We were super-scared on the road because of the black ice and just really poor conditions."
Local civil defence controller Chris Clark was also relieved the crashes were not a lot worse. About 30 passengers were on each of the buses. Clark said both volunteers and officials got cracking sorting out help for the shocked tourists.
"They opened up our event centre as an emergency civil defence centre, very grateful to have assistance from iwi, local rūnanga, who rustled up lunch for the people that were there.
"We also were very fortunate to have some staff from the Dark Sky Project in Twizel, who offered some of their Chinese staff to come down and help with interpreting."
Part of the touring party included one of the choirs that had competed at this week's World Choir games in Auckland.
Clark said passengers will be bussed to Christchurch on Friday, but on Thursday night were staying in a Twizel hotel.
"I think they collectively made a wise decision that they didn't want to be on the road in dark and possibly icy conditions again, so they were all holed up in a hotel."
Black ice warnings
New Zealand Transport Agency / Waka Kotahi had been warning about those icy conditions since Wednesday morning, saying drivers should also be aware of fog and possibly snow driving.
Instructor Mark Rivel Johnson said if drivers did hit ice, they should not brake.
"Any inputs in terms of speed reduction or steering [should be] gradual and gentle. You're generally better if you have the space available to decelerate and potentially come down the gears gradually rather than trying to brake."
Up until Thursday, there had been 11 fatal or serious crashes on the Tekapo-Twizel road. In the past five years, six people have been killed and 18 seriously injured.
'It's just almost invisible
New Zealand Institute of Driver Educators president Mark Revill-Johnson told Morning Report "black ice" was "probably a little bit of a misleading term" for it.
"All it is, is that you can see the road quite clearly through the ice, and it's just almost invisible. It usually forms around freezing point, although you can get ground frost from 3C. But when you get light rain onto a freezing road surface it freezes very quickly, and it's impossible to tell. You can't see it at all. So, it looks black because it's just showing the road surface."
He said "see-through ice" was perhaps a better term.
"Once your vehicle's lost traction then you have very little control over braking or steering. If your tyres have no grip on the road, you're essentially going in a straight line until it runs out of momentum. It's very difficult [to drive safely]. You have to try and anticipate where those conditions might exist… black ice looks quite shiny, and it's almost like a wet road looks, when you see the shiny patches on a wet road. It looks very similar to that."
Witness accounts put the buses at upwards of 100km/h. Revill-Johnson said even just 10km/h can be too fast on black ice - especially if it was foggy.
"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. So if there's fog around, you can't out drive your view because you're not going to see stuff that matters."
There was an ice warning out on Friday morning again - including State Highway 94, Mossburn to Milford Sound; State Highway 6, Makarora to Kingston; State Highway 8, Roxburgh to Omarama; State Highway 85, Kyeburn to Alexandra; State Highway 87, Kyeburn to Outram; and State Highway 8, Lake Tekapo to Omarama.
And in Wellington, officials warned drivers to take care due to fog causing low visibility.
Unfamiliar roads
It was still foggy in Twizel on Friday morning. RNZ reporter Niva Chittock told Morning Report visibility was probably about 100m - not quite as bad as Thursday.
"It's hard to see where the water starts and the fog ends, even so it'd be quite hard to see where you're going, especially if you don't know the roads," she said.
She said locals knew the stretch of road was dangerous, and can take visitors by surprise.
"The shrubbery on the side of the road had icicles hanging off it and you were driving in sort of one or two degrees - it's not going to be conditions that a lot of people might be used to, or might be prepared for. Because maybe one or two minutes further up the road, you'd be driving perfectly clear, sunny conditions, no ice on the road - and then you turn a corner into fog and into shade where the ice would be even at two, three o'clock in the afternoon."
Mackenzie District Mayor Anne Munro was yet to personally speak to anyone involved in the accidents.
"It's winter time, and when driving on the inland roads in Canterbury, Otago or Southland during the winter, you know, from time to time you experience these dreadful driving conditions, these challenging driving conditions that were experienced… I am assured that all the visitors that were involved in this accident have been well cared-for."
She said NZTA had signs and billboards up warning people to drive to the conditions. It would be up to the agency to decide whether to close the road, she said.
"From every situation comes learnings… I just encourage people to think about the fact that it is winter time and to be mindful and to drive to the conditions."
