Community resistance forces look at tunnels for $1b motorway

Transit NZ is sending a $1 billion-plus Auckland motorway project back to the drawing board - a move which could spare scores of homes from demolition.

The highways agency has decided to widen its range of tunnelling options for the 5km motorway extension from Mt Roskill to Waterview, after running into strong community opposition as well as geotechnical challenges around the sensitive Oakley Creek.

It confirmed yesterday that it was now considering three potential options for taking an undisclosed portion of the motorway underground, including a bored tunnel to minimise surface disruption.

That means a delay of up to a year in seeking a designation for land needed for the route, because of the large scale of extra investigations needed, although a softening of community opposition could shorten consenting procedures.

Residents feared an earlier proposal for a cut-and-cover tunnel would account for only a small section of the route and cause considerable disruption while being built into a shelf between Great North Rd and Oakley Creek.

They were also alarmed at plans for entry and exit ramps through the Phyllis St Reserve and sports grounds, above the creek, and the impact on pre-European and early colonial archaeological sites.

The proposed road would run almost entirely through the Mt Albert electorate of Prime Minister Helen Clark, who said last year that a "21st century" motorway required tunnelling through sensitive areas.

It will be the costliest component of Auckland's western ring route, which Transit views as its top national priority, and is needed to link State Highway 20 to the Northwestern Motorway.

But Transit chairman David Stubbs said yesterday that the Prime Minister had not sought to intervene in his agency's planning, which included a statutory requirement to consider community concerns.

Despite challenges posed for the project, which he regards as the country's largest and most important road proposal since the Harbour Bridge was built in 1959, he remained optimistic it could be ready by 2015.

His board has called for detailed investigations of three tunnelling prospects, including enhanced cut-and-cover options along longer sections of the route than proposed.

These include digging a tunnel under the section of the Waterview straight now covered by Great North Rd, to remove the motorway as far as possible from Oakley Creek, apart from two crossings.

But Mr Stubbs said the third possibility, a bored tunnel, raised the potential for a more direct route which could avoid zones where groundwater pressures or an ancient lava near Oakley Creek presented difficulties.

He said Transit would have little idea of the potential extra cost of a bored tunnel before completing its geotechnical investigations, and he would not predict how much of the route it could cover.

But Friends of Oakley Creek spokeswoman Wendy John said she was not alone in wanting a bored tunnel from Richardson Rd, at the end of the Mt Roskill motorway extension now under construction, to Waterview.

The original plan would have involved the destruction of about 300 homes, and measures proposed by Auckland City Council to reduce the impact on Oakley Creek would have been at the cost of demolishing a row of houses along Great North Road to make room for the motorway.

Some of the extra cost of tunnelling could be chalked off against lower compensation claims from property owners.

Council for Infrastructure Development chief Stephen Selwood accepted last night that resource consent delays may be reduced by a tunnel, but said Transit had begun planning six years ago and should have considered that option much earlier.