Martin Gummer says big projects need hard-headed analysis, not favouritism.

Recent political comment about two big transport proposals - the Puhoi to Wellsford Highway, and the CBD rail loop - are starting to frame them in polarised terms.

Urban vs rural, rail vs road, the working person vs the wealthy holiday home owner, Auckland vs Wellington wishes.

But this should not be the basis for choosing between them. Both are huge projects, with considerable risks, uncertainties and impacts. Both will have their day - but when?

And that poses another question. Are there cheaper ways of delivering similar results? Or, more realistically, are there much cheaper ways of delivering at least some - and sufficient for the meantime - benefits?

This is one big difference between the projects. The CBD rail loop is an all or nothing project. A loop that stops halfway is not a loop but a dead-end - or loopy.

The holiday highway, however, has a lower cost alternative - improvements to the existing road, that could defer replacement for a further 20-30 years. Corners could be smoothed, alignments improved, maybe a short bypass built around Warkworth, and three- or four-lane sections with a central wire barrier built in the Dome Valley.

To put it in perspective - the holiday highway will cost at least $1.6 billion whereas the entire Albany to Puhoi Highway (tolled and untolled), complete with tunnels and viaducts, cost about $500 million.

So what huge benefits justify spending four to six times greater than that for a major overhaul of the existing road? A time-saving of 10-15 minutes over the status quo? Hardly.

Undoubtedly the highway would reduce accidents and save lives and injuries. But couldn't most of these benefits be gained by analysing accident black spots and thinking creatively about how to reduce them within a budget $200 million or less?

Proponents of the holiday highway - especially the NZ Transport Agency - need to answer these questions. This agency is in the interesting position of being proponent of the project through its State Highways Division and having a boss who advocates it. But the agency also decides if it gets funding or not.

This is not beyond seasoned Wellington bureaucrats. But perhaps mindful of this challenge, the Minister of Transport seems to have taken the ball off them by reportedly declaring that the holiday highway already has funding allocated but the CBD rail loop does not.

If so, the question must be asked - why, how, when and by whom was such a momentous decision made? If they have similar transport benefit-cost ratios, how was one project favoured over the other?

The minister and the Government are getting into tricky territory here. This has more than a whiff of the politicisation of transport funding that characterises the Australian system.

If so, then the minister has to be prepared to deal with the proponents of other projects throughout New Zealand who knock on his agency's door. Unless he takes these two huge projects right outside the transport agency's funding allocation system, he risks undermining its integrity.

This will have widespread implications, not least for the Government's relationship with local government and its standing in many communities.

The CBD rail loop also requires hard-headed, analytical questioning of the cost estimates, the passenger patronage modelling results, and the economic benefits. Incidentally projects of such scale and impact, like Melbourne's Trans-Urban City Link, can and do influence a city's overall economic performance and this should be taken into account.

At $2.3 billion the CBD rail loop is a huge project and the confidence levels of the cost and benefit estimates need tough scrutiny - as do potential scope adjustments that could improve its viability.

We also need to know what the cost of subsidising extra rail services would be (net of reductions in the cost of existing services associated with increased system-wide patronage).

Both projects will have longer term, "transformational" effects. The most profound will be the impacts on land values, land use, property development and generated (induced) traffic.

The CBD rail loop should encourage urban renewal, commercial activity and property development along its alignment, and more intensified urban development around or near other rail stations - helping to harness Auckland's growth within its existing urban area.

It should also make rail travel a more viable, accessible option for more Aucklanders.

The holiday highway will further improve property values, increase property development in Warkworth, Wellsford and surrounding communities, and encourage more commuting from there to Auckland. Where do the Government's priorities lie?

Lastly, what part will the Auckland Council play in this decision? It is inconceivable that the new council should not have a major say on two projects with such big implications for its citizens, their quality of life and for Auckland's commercial development and urban form.

Martin Gummer was chief executive of the former national land transport funding agency Transfund New Zealand.