A plan to increase rail and shipping for New Zealand freight is getting the thumbs down from the Government.

The Greens want 50 percent of our freight off the roads within a decade, to reduce emissions.

That's the central point of the party's latest transport policy launched in Wellington today.

MP Julie-Anne Genter said the policy would also allow the transport budget to be used to fund rail projects, including setting aside $860 million for the electrification of rail lines between Auckland, Hamilton, and Tauranga.

"It's an ambitious target, but I think that it's a place to start," she said. "We've got huge amounts to gain from moving more freight on rail and sea, both in terms of safety, economic benefits and environmental."

Ms Genter said they'd take funding from roading projects that have low cost-benefit ratios.

She identifies a planned project for the Waikato Expressway, and the Puhoi to Warkworth road of national significance as potential candidates.

But Transport Minister Simon Bridges said the policy amounts to a major spend up on behalf of the taxpayer.

He said it would take a billion dollars a year of spending on rail, and would mean an increase of about 33 percent on road user charges.