The Green Party is backing Auckland's City Rail Link, saying getting people out of their cars and onto rail will reduce congestion on the roading network.
Co-leader Russel Norman told TVNZ's Q and A this morning that the rail loop will effectively double the capacity of the network.
The Auckland City Rail Link, which is estimated to cost of $2.86 billion, extends the existing rail line underground through Britomart, under Albert, Vincent and Pitt streets, then beneath Karangahape Road and the Central Motorway Junction to Symonds Street before rising to join the western line near Eden Terrace.
It would be built in two 3.5 kilometre long twin tunnels up to 45 metres below the city
Auckland Transport says it will need to purchase 210 properties, and the underground rights to a further 70, for the tunnels and stations.
Norman said combined with the electrification of rail lines it will create a much more efficient transport network in Auckland.
He said when Aucklanders are asked where they want the money spent "the priority is getting this rail loop finished so that we can actually have a decent transport network in Auckland".
And Norman claimed it was more financially beneficial than the Government's $12 billion "roads of national significance" project.
An upgrade of State Highway One from Puhoi to Wellsford features in the list of seven massive roading projects the Government wants completed within 10 years.
The Waikato Expressway, Tauranga Eastern Corridor and the Levin to Wellington stretch of SH1 are also on the list.
Norman said looking at the benefit-to-cost ratio the rail network comes out on the latest study at about five to one. He said Puhoi to Wellsford stretch could be made safer for a lot less than the Government's spending, and could be done faster.
Labour is pleased the Greens are backing the plan. Auckland issues spokesperson Phil Twyford said the link would open up the potential for trains every 10 minutes on the western and southern lines at peak times.
Labour has promised to fund half of the City Rail Link from the National Land Transport Fund by reprioritising planned motorway projects like the Puhoi-Wellsford holiday highway, with the expectation that Auckland Council would fund the other half.
Twyford says National focus on a 1950s model of sprawl, poor public transport and clogged motorways won't help Auckland prosper.
"Auckland is moving ahead. There is a real sense of progress. Unfortunately the Government is saying no to Auckland's transport priorities, and no to its plan to balance greenfields growth with intensification. Under Ministers like Nick Smith and Gerry Brownlee, Wellington is a dead weight holding Auckland back."
Labour says the high level of agreement with the Greens on Auckland's transport priorities means a Labour-led Government would move quickly to build the rail project.
"Today's announcement by the Greens will reassure Aucklanders that a future Labour-led Government will work with Auckland Council to deliver the transport infrastructure the city desperately needs," Transport spokesperson Iain Lees-Galloway said.
"Auckland's motorways need to be freed up to allow the efficient movement of freight. That can only be achieved by building reliable, regular and user-friendly public transport.
"The City Rail Link is a vital component of Auckland's public transport network."