The Government is set to unveil new details about light rail in Auckland which are understood to include significant tunnelling works putting the price tag in the region of $10 billion.
Transport Minister Michael Wood is expected to announce three shortlisted options tomorrow for the city's first light rail line running 22km from the central city to the airport.
The options are light rail, which runs at street level and mingles with traffic; light metro that runs down a dedicated route above or below ground; or a mix of light rail and light metro.
The Herald understands an indicative business case that has gone to the Government has a preferred option that involves tunnelling under the central city because of the lack of road space and to avoid years of disruption.
It has also been suggested tunnelling could continue further along the central isthmus before light rail runs above ground from Mt Roskill to Onehunga, Mangere and the airport.
"It's bloody complicated and they are big numbers," a source said.
An establishment unit set up by Wood in March has considered a number of alternative options for high-frequency rapid transit along the corridor, including heavy rail and trackless trams, but ruled them out in favour of light rail or light metro.
The unit has passed on the indicative business case with cost estimates to the Government for the Cabinet to make decisions on the next steps for light rail before Christmas.
It is believed the Government has decided to proactively release some details from the business case to gauge reaction following the public uproar over the $785 million cycle bridge across the Waitemata Harbour.
So far, the Government has only released sketchy details for what Wood has called "the largest and most complex infrastructure project in New Zealand".
Details about the mode, route, locations of stations and cost are still shrouded in secrecy. The Government has also gone from emphasising a fast route to the airport to light rail being a catalyst for shaping growth and development along the route.
Dominion Rd - Auckland's second busiest bus corridor - was initially envisaged as the street-level route through the isthmus, but Sandringham Rd has been added because of its proximity to large scale housing redevelopment by Kāinga Ora at the southern end.
The unit was also given the job of ensuring light rail is future-proofed at the city end for light rail to West Auckland and rapid transit to the North Shore, including a new harbour crossing.
Light rail has been a gnarly problem for the Government since Prime Minister Jacinda Ardern promised at the 2017 election to have the first leg from the CBD to Mt Roskill completed by this year and running all the way to the airport within 10 years.
Labour also promised in 2017 to build light rail to West Auckland but scrapped the idea in 2019.
Following a convoluted process last term that pitted the NZ Super Fund and a Canadian pension fund against the NZ Transport Agency to build light rail, a recommendation to go with the Super Fund's proposal was blocked by Labour's coalition partner NZ First in the middle of last year.
NZ First leader Winston Peters said the scheme would cost between $10b and $15b and lead to a "decade of chaos".
Former Deputy Prime Minister Sir Michael Cullen wrote two columns in the Weekend Herald just weeks before he died in August this year raising concerns about the enormous cost and disruption of light rail, suggesting electric buses would be a better solution.
The Labour Party elder statesman said light rail was an "idea whose time has passed", saying its supporters had dismissed the enormous cost and disruption and arrived at the solution before adequately analysing the problem.
The Government has set aside $1.8b for light rail in Auckland, but not said how it will fund the rest of the project. Auckland Council is not providing funding.
The Government is also being pressed to pour billions of dollars into Wellington's $6.4b transport package including a proposal for light rail from the central city to Island Bay.
National's transport spokesman David Bennett said it is unclear why Labour is returning to light rail when the eyewatering $10b price tag is a lot to throw at a something that is no faster than the buses currently on our roads.
"For a similar price tag Auckland could get itself a second, much needed, multimodal harbour crossing. This would be a much smarter strategic investment for our largest city.
"The congestion of the Dominion Rd/Mangere corridor does need addressing, but rapid bus transit could achieve this as has been the case on the North Shore. National would want to see these kinds of alternatives looked at before spending $10 billion on light rail," he said.