KiwiRail has announced it will replace its electric train fleet on the North Island main trunk line with diesel locomotives, a decision criticised as a big backwards step by the Green Party and Labour.
Peter Reidy, KiwiRail chief executive, said the fleet of almost 30-year-old electric trains that run between Hamilton and Palmerston North will be phased out over the next two years, and replaced with diesel locomotives.
He said electric infrastructure on the line would be maintained to allow for any future use.
KiwiRail considered replacing the electric fleet with other electric trains, upgrading the current electric trains, or replacing them with diesel trains.
Reidy said the electric trains that will now be phased out were breaking down too often. A "small number" of staff could be affected by the decision, he said.
The main trunk line in the North Island runs from Auckland to Wellington, and is electrified only between Hamilton and Palmerston North.
That meant KiwiRail was essentially running a "railway within a railway", Reidy said.
"The doubling up of service facilities, inventory, training and maintenance required with two separate systems on the line adds to the inefficiencies and unreliability," he said.
"We looked long and hard at the electric options and for our business, and most importantly our customers, they just did not stack up."
However, Green Party transport spokeswoman Julie Anne Genter said replacing electric trains with a diesel fleet was a "massive step backwards".
"National has promised to take climate change and transport issues seriously, but it's underfunding of rail is responsible for short-sighted decisions like this. National should commit to completing the electrification of the North Island main trunk line. This would send a clear signal to KiwiRail that they can invest in an electric future.
"New electric trains are cleaner, quieter, and have lower fuel and maintenance costs over their lifetime. They're also powered by local renewable energy rather than imported oil."
Labour's transport spokeswoman Sue Moroney said the decision meant National's new Cabinet was "already looking like a relic of a bygone era".
"Minister Simon Bridges has approved the daft decision, making his apparent commitment to increasing the use of electric vehicles to reduce carbon emissions look hollow and hypocritical."
"The electrification of the main trunk line between Hamilton and Palmerston North was a $250m "Think Big" project investment in the 1980s. The rest of the world is now following suit."