The Green Party wants a daily passenger train line between Auckland, Hamilton and Tauranga, using trains and tracks currently used for freight.
Under the policy, trains would run five times a day between Hamilton and Auckland, as well as once a day to and from Tauranga.
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The trains would be introduced on a trial base, starting in 2019. If the trial is successful, the Greens would roll out an upgraded service in about 2025.
Greens transport spokesperson Julie Anne Genter says the service would initially use refurbished existing Silver Fern trains that are currently not in use.
"Essentially we can get a trial passenger service going at very, very low cost within a year or two," Ms Genter told Newshub.
It's based on a plan released by influential public transport lobby group Greater Auckland, which proposes a three-stage rollout to introduce regional rapid rail to the upper North Island.
The Greens have committed to a five-year-trial, but say all three stages "make perfect sense" in the long-term.
However National Party Transport spokesperson Simon Bridges says regional rapid rail supporters don't understand how much these plans will actually cost.
"It seriously underestimates the capital infrastructure costs involved," he says.
"That said I'm on the record and being very open because I am about trialling commuter rail, particularly Auckland and Hamilton.
"What it requires is a business case process really to go through the details and see how a trialling of some of these things could possibly work."
Mr Bridges said he was open to trialling some commuter rail further south, as the population shifted.
"I think though that is a different proposition and a much smaller one where the benefit cost of the programme potentially can make it, as opposed to a much more significant rapid rail regional rail network," he says.
Ms Genter is confident a rail network would help give people more options for affordable places to live.
"We're going to be enabling people to move around more freely. People will be able to work on the train. They will have more housing options and commuting options, if that's what they choose.
"When you put in a frequent rapid train line it becomes much more attractive to live further away from the city."
She says the service between Auckland and Hamilton will take around two hours and 15 minutes, with the train to Tauranga taking around three hours and 30 minutes from Auckland.
An upgraded faster service would cost about $400 milllion, with $78 million of that spent on track improvements the Greens say.
It normally takes around 90 to 120 minutes to drive between Auckland and Hamilton, depending on the traffic.
The commuter line to Hamilton would not be able to run until a third main line is built in Auckland - which should be completed in about 18 months, a Greens spokesperson said.