Hobson Bay has emerged as the most likely route for the Auckland end of a 27km eastern highway to Manukau, amid engineering and cost concerns about tunnelling through Parnell.

Auckland City Mayor John Banks acknowledged yesterday that this was the most contentious sector of a project on which he and Manukau Mayor Sir Barry Curtis have staked their mayoralties.

But he said scrapping the tunnel in favour of a four-lane expressway across Hobson Bay - and jettisoning proposed buslanes parallel to the railway line from Panmure to Britomart - could shave $1 billion off a $3.5 billion development bill.

Mr Banks said a 3.5km tunnel from Shore Rd to Carlaw Park, which he previously favoured as more environmentally sellable, would have an almost open-ended price tag when allowing for massive roundabouts called gyratories at each end.

Engineers said these would be required to prevent queues of traffic jamming the tunnel, but they would create other risks and experts from as far as London and Australia had warned the option was technically doubtful.

"In a perfect world where we are pumping oil out of the ground somewhere in the back of Glen Innes we may be able to fund all these things, fix all these problems and money wouldn't be a problem," he said.

"But we are into providing an eastern corridor which is sound, sensible, reasonable and fundable."

A steering group of Auckland, Manukau and Transit New Zealand representatives came out earlier yesterday in favour of a Hobson Bay crossing but decided to leave a final decision to his council at the end of next month.

Mr Banks said that given the unanimity of the group's preference, he would be surprised if the council decided otherwise.

The group also indicated a desire for the highway section across the bay to be "something substantially less than the huge engineering structure we have heard proposed".

Opus International Consultants proposed in March two general traffic lanes and a dedicated bus lane in each direction on bridges next to the rail embankment across much of Hobson Bay, Orakei Basin and up Purewa Creek, with a pedestrian and cycleway alongside.

But the steering group now favours scrapping the buslanes and encouraging passengers to transfer to upgraded and electrified rail services from Panmure to Britomart, even though the Opus report claimed it may be difficult to persuade them to switch over.

Project director Grant Kirby listed pros and cons of both tunnel and bay options in a report to the group.

Advantages of a bay crossing included better strategic connections to central Auckland, the state highway network and the port.

Minuses included significant environmental, visual, noise and community acceptance issues, alignment impacts on port and rail land, and stability concerns across the bay and basin, "particularly having regard to earthquake conditions".

Mr Kirby said a significant amount of land reclamation would be needed, which could be a high risk, even though it would markedly improve the Tamaki Drive environment for recreational users.

"This is a major regional and national attraction," he said.

But he acknowledged that because of direct connections to the port, a bay crossing would entice large volumes of trucks to use the eastern highway next to a relocated Tamaki Drive, which would run along the seaward side.

It would also cause a significant adverse impact to the Outboard Boating Club, which has about 1800 members and 220 vessels berthed at its marina.

Ports of Auckland chief executive Geoff Vazey welcomed any project which helped to complete the region's roading network but stopped short of commenting directly on the Hobson Bay option, except to say it was unlikely to require much port land.

But the boating club said it would be hard to survive on its existing site unless Mr Banks pursued a suggestion that the highway be buried in a "cut-and-cover" tunnel under its headquarters.

Its lawyer, Paul Cavanagh, QC, said the club did not want to stand against the project but wanted the councils to recognise its growing importance as the region's largest and best facility for a growing boating community.

He said the club would be hard-pressed to find an environmentally acceptable alternative site and suggested the councils concentrate on completing the State Highway 20 western bypass as a better way of battling congestion.

Tamaki Drive Protection Society committee member Eddie Mann said that although some of his colleagues supported an eastern highway, he was seriously concerned about congestion when traffic reached the Auckland end.

It was also disappointing that a highway may be built through the middle of Hobson Bay just as Watercare Services planned to bury the 90-year-old sewer line across it at a cost of $47 million.

Hobson Bay Residents' Network co-ordinator Christine Caughey said a highway across the bay would be devastating for Auckland and called for a concentrated push to electrify the rail system.

Herald Feature: Getting Auckland moving

Related information and links