Auckland trains explainer: What is causing the heat issues on the tracks?

Train services around Auckland are facing delays and cancellations over the next few weeks due to hot weather. Photo / NZME

As the hot summer temperatures continue to stay around the mid to high 20s, so too do the worries around Auckland’s train services, which are set to face delays and cancellations over the next few weeks due to heat issues on the tracks.

One transportation expert says KiwiRail’s move to apply speed restrictions on parts of the metro network may be an “overkill” reaction.

The issue began on Monday afternoon when 80 trains were cancelled, massively delaying commuters trying to get home. The daily high was 25C.

Auckland Transport lashed out at KiwiRail over the issue, saying the speed restrictions and associated disruption would not have been necessary had KiwiRail attended to numerous faults on the network.

Director of public transport Stacey van der Putten said the issue was “decades in the making” and would take renewed investment and commitment to avoid in the future. She then warned of the likelihood of further disruption over the coming days.

On Tuesday, commuters faced further disruption. The Herald spoke to several who vented their frustration at being stopped from getting home.

“I’ve been waiting nine months for the [Eastern Line] train to return to service. Well, there’s been no improvement,” one said.

Another said: “I looked at the [timetable] noticeboard and saw all the cancellations and thought, ‘typical’”.

Auckland University’s Dr Timothy Welch - who specialises in transportation, infrastructure and urban modelling - says it is expected that infrastructure, or train tracks, can withstand a much higher temperature before buckling.

“Often the engineering standard is 60C to 65C before it starts to experience buckling,” Welch said.

Earlier this week, KiwiRail authorities announced the speed restrictions as track temperatures had reached up to 48C.

‘We’ve had hotter days and haven’t seen closures before’

“Likely it’s just overkill and it’s not going to happen again. But the reality is, we’ve had much hotter days and we haven’t seen closures before,” Welch said.

“So I wouldn’t expect it to happen going forward - or hope it wouldn’t happen going forward. I guess it’ll just mostly be dependent on what the weather does.

“But it does beg us to ask the question ... is this going to be something we have to deal with every summer?”

Train commuters are being warned to expect delays or cancellations that could last until next month. File photo / Greg Bowker

Welch said the density of the steel train tracks absorbed a lot more of the radiated heat or sunlight - which then causes the steel to heat up, even though the air temperature is lower.

“Essentially, [it’s like] when you walk outside, the old expression goes: ‘It’s so hot outside you could fry an egg on the pavement.”

Explaining further, he said the tracks had expansion joints that could effectively react or change in extreme weather conditions - either when it is very cold or very hot.

“If you look closely, [the track] has metal teeth, essentially. And they can separate when the structure is cold.

“When the steel gets cold, it contracts and when it heats up, it expands - just like water does. So it has room to grow.”

Earlier rail lines or tracks had a joint or connection between the next set of rail and plenty of space for those rail lines to expand as they heated up in hot weather.

But with modern rail lines, the length of the track is much longer before there is a break, Welch said.

“So when they heat up ... they still expand and what could really happen is that it could cause buckling - so the tracks kind of become wiggly. That could technically lead to a derailment of a train.”

He said they dealt with that issue by nailing the tracks to the ground and using a much stronger connection because the steel can handle expanding without breaking and buckling.”

Welch also acknowledged that there were other train tracks around the world built to withstand higher temperature variants.

“There are rail train lines that run through the centre of Australia, through the centre of the Sahara Dessert ... with extreme environments that can withstand temperatures.”

Dr Douglas Wilson, associate professor and director of the Transportation Engineering Laboratories in the Department of Civil and Environmental Engineering at Auckland University, said today’s situation is due to a lack of maintenance over about 30 years.

“When you have this hole of a gap for 30 years of under-investment, it’s very hard to actually improve the network as well as upgrading the existing asset that you already have.

“You can’t just do a small plaster covering. You’ve got to actually reinvest in the whole infrastructure - and a lot of it is rebuilding it from scratch because we didn’t maintain it during that period.

“You don’t maintain your car - you’re going to end up with a bigger problem.”

Vaimoana Mase is the Pasifika editor for the Herald’s Talanoa section, sharing stories from the Pacific community. She won junior reporter of the year at the then Qantas Media Awards in 2010 and picked up the best opinion writing award at the 2023 Voyager Media Awards.