Passenger rail would run five times a day between Auckland and Hamilton with one return service to Tauranga under Green Party policy.

The party said it would trial the service from 2019, and expects travel time to be about 2 hours 15 minutes between Auckland and Hamilton, and 3 hours 30 minutes from Auckland to Tauranga.

However, Green Party transport spokeswoman Julie Anne Genter said if the trial is successful the party would look at creating a premium service that would be quicker - around 1 hour and 15 minutes between Auckland and Hamilton.

The service would be great for commuters, Genter said.

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"I expect a lot of people from Hamilton and Tauranga will be attracted by the idea of being able to work and rest while on the train, and avoid Auckland traffic once in the city.

"There's been a lot of talk about passenger rail to Hamilton. We now have a plan to make this happen in our first term in Government."

The policy is based on a concept from the lobby group Greater Auckland. The Greens said the trial of the service would cost $20 million over five years, with the money coming from scaling back National's plans to spend on motorways.

"If this trial is successful, we'll look at creating a premium, fast service that would be about an hour quicker. This is estimated to cost around $400 million and could start in 2025," Genter said.

Transport Minister Simon Bridges last year said an Auckland-Hamilton commuter rail service could happen with some subsidies from regional and local councils. However, that was some way off, given the economics didn't currently stack up and work was dependent on the electrification of the Auckland railway lines to Pukekohe.

Outgoing Labour MP Sue Moroney has been a strong advocate for an Auckland-Hamilton service. The Hamilton-based MP has accused the Government of using electrification as a delaying tactic.

Last year the Green Party announced policy including electrifying rail between Auckland, Hamilton and Tauranga at a cost of $860m.

That is part of the party's plan to get half of New Zealand's freight moving by rail and sea within 10 years.