The Government's flagship light rail project in Auckland looks set to cost at least $15 billion, with a good chance the price tag will rise.
Transport Minister Michael Wood has unveiled three shortlisted options for the 22km light rail route from the central city to the airport with indicative costs of between $9b and $16.3b.
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; and a tunnelled option which is a hybrid of the two.
An establishment unit set up by Wood in March to get the troubled project back on track, has recommended the tunnelled option to the Government costing $14.6b, not light rail costing $9b and light metro costing $16.3b.
These costs are "indicative" and have a 50 per cent chance of rising once detailed design work is undertaken.
The unit also considered a number of alternative options for high-frequency rapid transit along the corridor, including heavy rail and trackless trams, but ruled them out.
The proposal to tunnel from the central city and through the isthmus to Mt Roskill has several advantages. It gets around limited road space, avoids years of disruption to businesses and gives flexibility to connect with high-speed transit from the North Shore and West Auckland in future.
The tunnelled option would begin at Wynyard Quarter, have stops in the central city and near the university campuses and a total of 18 stations, many of which will not be known until the detailed design stage.
From Mt Roskill, the tunnelled option would run as a light rail line alongside State Highway 20 to Onehunga, Mangere and the airport.
The establishment unit has presented an indicative business case for light rail to Wood and Finance Minister Grant Robertson, along with Auckland Mayor Phil Goff and deputy mayor Bill Cashmore.
Cabinet is due to decide before Christmas whether to proceed with light rail, what option to adopt and the next steps forward.
If the Government proceeds, it will be at least two years before a detailed business case, design works, consents are completed and there are shovels in the ground. Construction is expected to take 6-8 years.
Public consultation by the unit found strong support for quality mass transit, but concerns were raised about disruption during construction, an issue that has caused great financial and mental stress for businesses affected by works in the city for the $4.4b City Rail Link.
There were also concerns in places like Māngere that light rail could lead to gentrification - this is already happening at Māngere Bridge - and environmental, cultural and heritage impacts.
Wood said the business case concludes that light rail is a necessary investment to lessen congestion and future-proof Auckland, saying it will support more housing and give people real transport choices.
"It will provide the base and first stage of the additional Waitematā Harbour crossing and a line out to the northwest, beginning a city-wide transport network, so it's important that we make the best decision for the long term.
"We're being open about the pros and cons across the options, like disruption to businesses, value for money, the shape of our public transport network, and the ability to open up housing along the corridor in Mt Roskill, Onehunga and Māngere. These will all be factors we consider before making a decision," Wood said.
Mayor Phil Goff, whose support for light rail goes back to his days as the Labour MP for Mt Roskill, said the rapid transit corridor will enable more housing and job growth the city needs.
"This area will cater for an additional 66,000 homes housing nearly a quarter of Auckland's population growth over the next 30 years. It already provides a quarter of Auckland's jobs, connecting the two biggest employment hubs in the city," he said.
Light rail has been a gnarly problem for the Government since 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.
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 saying light rail was an "idea whose time has passed".
Its supporters, the Labour Party statesman said, had dismissed the enormous cost and disruption and arrived at the solution before adequately analysing the problem.