Ministers have announced an urgent review of KiwiRail after major disruption to train lines in Wellington this week.
Train services in the capital were drastically cut back after the breakdown of a specialist rail track evaluation car.
It prompted speed restrictions of 70kmh, with just half as many services as usual during peak times.
Transport Minister Michael Wood today called KiwiRail to the Beehive to provide an explanation on what happened and the plan to fix it.
In a statement this afternoon he said the disruption was "not good enough and follows other similar instances of service disruptions to commuters on KiwiRail's network".
"KiwiRail have accepted responsibility for the missteps which will result in further disruptions to services this week, and have reassured me they are acting quickly to restore fully functional services for commuters."
State Owned Enterprises Minister Duncan Webb said he had ordered an independent review into the operator, which would look into causes of the disruption across the country but largely focus on Wellington and the maintenance problems with the safety equipment.
Webb expected to appoint a reviewer this week, with findings to be reported next month, saying the review was "vital to public confidence".
The government had invested $8.6 billion into the rail network since 2017, with much of that going towards replacing track, installing new culverts and bridges, and upgrading turnouts, he said.
The government last week also announced 18 new trains for the Wairarapa and Kāpiti Coast lines to support express peak services and attract more commuters.
Speaking to reporters after the week's Cabinet meeting, Prime Minister Chris Hipkins said it was a core responsibility for KiwiRail to maintain the tracks and deliver timely and reliable services - and the disruption this week was not acceptable.
"Clearly they've dropped the ball here," he said.
"Billions of dollars over the time that we have been in government have been put into KiwiRail for things like track maintenance. Lack of funding isn't an excuse and so if they have one piece of machinery that they're reliant on, one would think that they would have made taken steps to make sure they've got some backup."
He said he would not expect government ministers to know whether there was one or multiple machines to check the tracks, and KiwiRail should be accepting responsibility.
"It's absolutely fair to say that over a long period of time - several decades - our rail system has been run down. Our government has put billions of dollars into upgrading the rail network.
"I wouldn't expect to be seeing the sort of disruption that Wellington commuters are currently seeing as when we have invested such a lot of money into improving maintenance and reliability."
Wood told Checkpoint the machine had been operating for 41 years without problems but KiwiRail had got it wrong in this instance with regards to their scheduling and rostering.
"It has led to this outcome so that's what needs to be fixed."
The government has provided extra funding so a new vehicle can be ordered.
"But irrespective of that this shouldn't have happened - there were errors that were made. It needs to be very clear what happened and steps need to be put in place in the organisation so we don't have a repeat."
Asked why buses, trains and ferries could not provide reliable public transport services around the country he said it was critical that improvements were made to lessen congestion on the roads and reduce the country's carbon emissions.
"I think when there are unforced errors like this one that's what really frustrates people."
The government was pouring money into trains, including for Wellington, and it was essential infrastructure providers like KiwiRail provided the reliability commuters deserved.
KiwiRail will co-operate fully with the government review, chairperson David McLean said.
It has also accepted full responsibility for the disruption which was unacceptable.
The track evaluation car had been repaired and should complete its assessments of the Kāpiti Line by Tuesday night with the speed restrictions to be lifted later this week.
"We take safety extremely seriously at KiwiRail and the speed restrictions mean potential safety risks are being managed, but we know Wellingtonians want this situation resolved as soon as possible and to never happen again.
"The KiwiRail team shares that view, and we will learn from this mistake."
Mayor sceptical
Porirua mayor Anita Baker said she would believe services would return to normal later this week when she saw it.
"Am I confident? No. I think people will just have to wait and see what happens. Usually Mondays and Fridays we find are quieter because people do work from home, but tomorrow I'm sure the roads are going to be absolutely hectic."
It was clear Wellington's public transport was not up to scratch, she said, noting problems were likely to persist for a few years yet.
"Driver shortages for the buses, Greater Wellington say that won't kick in and we won't see much change until September," she said.
"People have got bus cancellations and then they've got train cancellations ... it's not satisfactory at all."
Meanwhile, Hutt City mayor Campbell Barry said the blunder had dimmed the government's announcement that it would buy 18 new trains for the lower North Island.
He said the disruption was unacceptable, and would drive people back into their cars.
"I think it's unfortunate for KiwiRail that this has overshadowed the good news in the Budget for the new trains which will be operating in the region," he said.
"It really is a bit of an own-goal."
Residents wanted reassurance that rail networks were being managed appropriately, Barry said, and that there was a back-up plan when things went wrong.