It would cost close to $30 million to cover the subsidy, which could benefit up to 350,000 people in universities and polytechnics.
Students already get some subsidised travel on bus and train fares - up to 35 per cent in Auckland. But student unions have long called for a greater subsidy because public transport costs can swallow up to a quarter of a weekly student allowance or student loan entitlement.
Greens co-leader Russel Norman said the policy covered only off-peak hours because making trips free at all times could swamp the public transport network. Patronage was predicted to swell by at least 30 per cent if free off-peak travel was introduced.
The proposal was announced as part of the Greens' transport policy during the polling window for the latest Herald-DigiPoll survey.
The Greens are the biggest winners in the survey, rising nearly 4 points to 13.7 per cent of the party vote. That would translate to 18 MPs in Parliament, including five new faces.
The new MPs would be James Shaw, Marama Davidson, Barry Coates, John Hart and David Kennedy. Sitting MPs Dave Clendon and Steffan Browning would be re-elected.
The party has run a mostly faultless campaign with extensive door-knocking and regular policy announcements, including a new top tax rate of 40 per cent to raise $1 billion for child poverty measures and $1 billion in tax breaks for innovative businesses.