A 2016 video by Auckland Transport shows the proposed route of light rail line to the airport, later taken over by NZTA.

An unlikely alliance of six Auckland lobby groups is demanding more transparency about tightly-held plans for light rail in the city.

The six have jointly written to ministers, wanting details of the two different proposals which Cabinet is due to consider in February, two years after light rail was taken out of Auckland hands by the Labour-led government.

The call has come from the Automobile Association, Bike Auckland, the Employers and Manufacturers Association, Generation Zero, Greater Auckland and Heart of the City, which wants early public input.

"This is a once-in-a-generation project that will impact on lives of all New Zealanders, now and in the future, and the consequences of not getting it right would be enormous," they wrote, to senior cabinet ministers, the Prime Minister and the head of the Ministry of Transport which is running the selection process.

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The group argued that by not revealing details at this stage, or involving consultation, the eventual light rail scheme might be rejected by the public, or even face legal challenges.

None Artist impression of Auckland Light Rail trains en route to the Airport.

A light rail project from the CBD to Mt Roskill and on to Mangere and the airport, was well advanced by the council agency Auckland Transport, when the incoming Labour-led government promised to fully-fund it, and moved the work into the transport agency NZTA.

Soon after, in 2018, an unsolicited bid was launched by NZ Infra, a partnership between the Super Fund, and Canadian funder CDPQ, involving a private-public joint venture in which the funders would own the scheme.

Little information has been reached officially about the long-running process, with most of the details made public in a large leak to Stuff in October.

Chris Skelton/STUFF Transport Minister Phil Twyford and Auckland Mayor Phil Goff will reveal more about light rail in February.

NZTA has publicly admitted it "could have and should have" done better on managing the project, which the Transport Minister Phil Tywford took away from the agency and gave to the Ministry of Transport to weigh-up the competing bids.

"We urge you to provide key stakeholders with the opportunity to give feedback prior to binding decisions being made," said the six organisations, asking to be part of wider consultation.

In an interview with Stuff last week, Twyford said the next step would be to choose the preferred partner, and set out the funding approach.

"Who, and not what, is the decision that will go to Cabinet in February, then Cabinet will select the partner and the delivery model, then more work will be done on route alignment and design," Twyford told Stuff.

Auckland Mayor Phil Goff is happy about leaving that decision to the Government.

"Selecting the partner is the Government's role because it is the paymaster," he told Stuff.

Supplied/Auckland Transport Artist impression of Auckland's proposed Light Rail route on Dominion Road, Balmoral

"The council and Auckland Transport are involved in evaluating aspects of the proposals being put up, and Auckland Council will be on the overall evaluation panel, so we are involved in the process," said Goff.