The Green Party is promising free public transport for students and people under the age of 19.

The party will create a "Green Card" for free public transport to everyone under the age of 19 and people on a disability benefit.

Students at university, polytechnics and in training establishments, including apprentices, will also qualify for free, off-peak public transport, the party said at a transport policy launch in Auckland today.

The Green Card will cost $70 million to $80m a year - the cost of just 1km of National's motorways, said Greens transport spokeswoman Julie Anne Genter.

She said transport costs for a family were almost $40 a week higher than they were in 2013 with transport now representing 15 per cent of household spending at $195.

The Green Card would reduce the cost of a weekend outing for a couple with three children from Albany to the CBD from $40.22 to $19.40 and from Lower Hutt to downtown Wellington from $30.30 to $16.32.

The existing Gold Card for free public transport by older people will continue under the Greens.

The Greens also committed to building a congestion-free network in Auckland over the next decade, including modern trams, known as light rail, from the city to the airport by 2021, a Northwestern modern tram line, and begin work on rail to North Shore by 2030.

Green Party leader James Shaw says one in three kids gets dropped off at school by drivers and believes the policy would make a massive difference to congestion.

"Building the congestion-free network will be funded by reallocating existing low-value and non-urgent transport spending," said Genter, whose party plans to defer an east-west highway through Auckland's industrial belt costing up to $1.8 billion and the new Mill Rd four-lane highway from Manukau to Drury.

"We support allowing Auckland to raise a regional fuel tax. We will also work with Auckland Council to investigate part-funding some projects through land value capture," Genter said.

She said the party would announce more transport policies for other parts of New Zealand before the election.

Greens candidate Chloe Swarbrick said free public transport would help students struggling with the cost of living and reduce stress.