How State Highway 94 to Milford Sound is made safe for its million visitors

A helicopter swoops over the mountains above the Milford Road and drops explosives. Snow and ice cascade down, and when everything has settled, the area is much safer for the hundreds of thousands of visitors who will use the road below.

Each year, close to one million visitors travel the remote and rugged State Highway 94 from Te Anau to Milford Sound to reach the popular tourist destination in Fiordland National Park.

But behind the postcard-perfect scenery of glaciers, steep cliffs and waterfalls lies a high-stakes operation to keep the road open and safe no matter the weather, including using explosives to trigger avalanches before nature does.

The Milford Road Alliance, a partnership between the NZ Transport Agency and Downer, is tasked with managing the 120 kilometre stretch of highway that winds through the national park.

A dedicated team of 27 people work all year round to ensure travellers get to and from Milford Sound safely.

Alliance manager Kevin Thompson said the fairly short length of road presented a lot of challenges.

"We have the avalanche programme, we have rockfall issues, we have the Homer Tunnel, we have the alpine fault, we're operating inside Fiordland National Park, and we have a very large number of tourists who visit Milford Sound both New Zealand and international visitors," he said.

"All of those things wrap together to be quite a challenging environment."

Among the team's most specialised tasks is managing the risk of avalanches. Each winter, snow builds on the steep slopes above the road, creating hazards that could bury the highway without warning.

"Fiordland is an interesting place and it's why visitors from overseas come here, it's dynamic, it's a big landscape. The avalanches we get here are some of the biggest in the world if they get up to their maximum and it's because of the big valleys we have," Thompson said.

"We can have avalanches that start way up high, they come to the edge of the cliff and then go into freefall and land on the road. Not a lot of time or chance for people to get out of the way or survive those big ones, so that's why we have to use a number of methods to try and prevent them starting for the first case, or keep people away if we can't deal with them ourselves."

The avalanche control programme was established in 1983 to predict and manage risk from snow, ice and avalanches more effectively.

"Every winter is different, this winter we didn't get avalanche hazard on the road until, really, the end of August," Thompson said.

When the snow builds to dangerous levels, sometimes the team uses explosives to trigger avalanches.

"Explosives are something we don't use all the time but when we do we will direct those where needed. So explosives we will drop into the avalanche zones that are the highest risk and we'll bring down avalanches as much as we need to. The aim there is to try and bring them down before nature brings them down so we can control that process," Thompson said.

Milford Road Alliance operation lead Brad Carpenter said the conditions had to be right to use explosives.

"We have to have flyable weather to get the helicopter to do that. When the conditions warrant, it takes a lot of background experience even prior to getting to working at the Milford Road, so when we're hiring people we look for pretty extensive experience using explosives in more ski area settings," he said.

Spring adds another challenge, as rising temperatures destabilise the snow just as tourists return in large numbers. September through to November was usually the riskiest period for avalanches, Thompson said.

The team shifted focus when it turned to summer.

Summer was a time to maintain equipment, maintain the road and infrastructure and carry out tree work to keep the road clear of trees and debris. The team also calibrated their network of weather stations, which fed into avalanche forecasting alongside MetService data.

"What we really want people to be left with is a trip to Milford Sound where they have no delays, everybody is in and out safely and we don't interrupt or affect their visit. That, for us, is what we aim for where we don't impact their trip, they have a safe visit and they don't even know we do our job," Thompson said.

He said a warming climate was adding new challenges.

Avalanche zones were being exposed to more rain and warmer temperatures, making the snow more unstable. The risk of rockfalls and trees falling was also increasing, Thompson said.

"We are expecting far greater numbers into the future into Milford Sound over the coming years so tourism is predicted to increase. That's going to bring some interesting challenges for us as a team to manage and be part of. We are looking forward to that, that's going to be an exciting challenge. That said, we are going to be dealing with nature and that's changing too."

Sign up for Ngā Pitopito Kōrero, a daily newsletter curated by our editors and delivered straight to your inbox every weekday.