Key Points:

When she was chief executive of the Auckland Regional Council Jo Brosnahan's role was, among other things, to protect and preserve Auckland's environment.

Now she has changed hats and as a member of the Minister of Transport's advisory group on roading costs is berating state road builder Transit New Zealand for wasting money on mitigation.

The report of the ministerial advisory group (MAG) criticises Transit for unjustified costs involved in scrapping overland highways at Albany and Victoria Park in central Auckland in favour of more costly tunnels.

As far as the Alpurt B2 project north of Albany is concerned, this criticism is academic as the project is safely under way. But the thought that the yet-to-be-built Victoria Park tunnel proposal might now be relitigated is alarming. Particularly when you examine the shaky reasoning of the advisory group's conclusions.

For two years from 2002, Transit NZ argued for the cheaper, overland solution of replacing the flyover with a $160 million viaduct of twice the existing road's capacity.

Auckland City and regional council politicians fought for an underground solution, arguing that the impact on the inner-city park of the above-ground solution was unacceptable.

The road builders listened to the arguments and finally, in December 2004, came up with a compromise. Transit would leave the viaduct in place for southbound traffic and build a $200 million tunnel (at last count $320 million) for traffic going north. It didn't rule out the possibility of a further tunnel to replace the flyover at a later stage.

The ministerial group says Transit's reasoning for accepting the underground solution was flawed. It writes: "An objective assessment of environment effects prepared in September 2002 for Transit NZ showed that Option D (northbound tunnel option) retains the status quo within Victoria Park and therefore has no significant reduction in effects compared to Option A (the viaduct option). On this basis, there appears to be no objective rationale for committing the additional funds required to build Option D over Option A."

The report goes on to opine that "analysis indicates that significant environmental improvement will only occur if all traffic is moved underground".

To me, it's the advisers' reasoning that is flawed. We can all agree that burying a one-way tunnel alongside the existing viaduct will retain the environmental status quo, apart, perhaps, from the tunnel exhaust fumes vented overhead. But how on earth can they argue that replacing the existing flyover with one that is twice the size and carries twice the amount of traffic will not have a significantly increased environmental impact?

The only encouraging note is the concession that although the Government funding agency Land Transport NZ "has only committed design funding" for this project, "it is the general understanding of Aucklanders that a tunnel will be constructed. It would be very difficult for Land Transport NZ to resile from this position."

The Wellington bureaucrats and politicians had better believe that. Auckland will be in uproar if the viaduct option is revisited.

The Land Transport Management Act 2003 calls on the road builders to give greater consideration to economic, social and environmental issues than they used to, and Aucklanders will hold them to it.

To give Transit NZ its due, I'm sure this requirement encouraged it to adopt the tunnel solutions, both at Albany and Victoria Park. It's also a likely solution to the vexed problem of the Waterview end of western ring route.

The MAG report seems to pine for the days when the road must get through at all costs. Concerns about the environment are seen as a weakness. It claims, for instance, that at Albany, Transit NZ included "environmental enhancements" costing $65 million "in response to the risk" that local activists would delay the project by opposing it through the courts.

This is unfair. The Transit board abandoned the "cheap" option to drive a huge cutting through unstable, bush-covered land because members realised it was a recipe for environmental catastrophe. Apart from the impact on the immediate environment, it risked washing huge quantities of silt out into the adjacent Hauraki Gulf Marine Park.

Transport Minister Annette King says the report is part of the Government's desire to achieve roading value for money. Fair enough. But the days are long gone when the Government road builder could point his bulldozer in the desired direction and put his foot down. Transit NZ appreciates this.

It's a pity the advisory group has not kept up with what's acceptable.