Armies of roading designers are finalising bids for Auckland's $1.85 billion Waterview motorways project, which has won approval in principle.

Although a Government-appointed board of inquiry has yet to grant final approval, a draft decision has given the Transport Agency confidence to confirm a deadline of June 16 for bids from two rival contracting alliances.

Led by local firms Fletcher Construction and Fulton Hogan in partnership with Australia's Leighton Contractors, each has had teams of about 150 designers and engineers preparing plans since November for New Zealand's largest roading project.

Although the board's final approval of 54 resource consents and six route designations between Mt Roskill and Te Atatu is not due until the end of next month, it is unlikely to contain other than minor changes to this week's 390-page document.

The agency's state highways manager for Auckland, Tommy Parker, said yesterday that the draft meant his organisation could "proceed with certainty" towards awarding a contract by late August for a pre-Christmas construction start.

Transport Minister Steven Joyce said that though not wanting to be seen to be in any way influencing the board's final decision, he was "cautiously excited" about completing Auckland's western ring route.

He believed a balance had been "pretty nearly struck" between the costs of such a large venture and environmental protections for the
communities along the proposed mixed surface and underground motorway, and a widened Northwestern Motorway.

Despite at times fierce opposition to various proposals since consultations began in 2000, community groups say the board's decision largely meets their concerns.

"If a motorway must be built, this is the way to do it," said Albert Eden Local Board deputy chairwoman Margi Watson, a Waterview resident and long-time opponent of the project.

Bill McKay of the North West Community Association and Living Communities called the decision fair and urged the Transport Agency not to challenge up to $50 million of environmental enhancements prescribed by the board.

These involve altering the locations of two large tunnel emissions venting towers, and contributing $8 million to a cycling and pedestrian pathway between Owairaka and Waterview.

Although the agency opposed these items at a marathon public hearing, Mr Parker yesterday ruled out appealing against them.

"We are not authorised to challenge any of the broad conditions - we can only challenge on issues of law," he said.

He hoped the two design teams would find ways of minimising the extra costs.

The board has stipulated that the towers must be 15m high, as opposed to earlier proposals for 25m structures at each end of a pair of tunnels covering 2.5km of a new 4.5km motorway.

It is also requiring the northern tower to be built on the other side of Great North Rd from Waterview Primary School, and the southern structure to be partly submerged on a site away from a narrow neck of Alan Wood Reserve in Owairaka.

The board said the shared pathway, which is to include two foot bridges across the western railway line and Oakley Creek, was needed to mitigate lost open space at each end of the tunnels.

It has also prescribed a skateboard rink and BMX bike track for a realigned Waterview Reserve.