Key Points:

National Party leader John Key might have got away with sending transport spokesman Maurice Williamson to the naughty stool for blurting out the inconvenient truth about plans to toll Auckland motorists, if it had happened only once.

But he must think we're idiots if he believes we'll fall for him trying to pass off Mr Williamson's repeat performance as just another case of the overexcitable veteran not taking his pills.

In August, Mr Williamson said he didn't know anyone who would mind paying a $3 to $5 toll each way if it was going to save them 40 minutes of commuting time. Mr Key slapped him down, saying a more "realistic" toll would be in the vicinity of $2.

On Monday, Mr Williamson couldn't resist adding that this $2 might rise to $3 for "very long-haul roads". His reward was another leader's red card and the broad hint that any hope of his returning to the transport portfolio, if National won, was zilch.

Mr Key said his colleague had broken the Key principle that to be appropriate, "tolls have to be affordable ... to provide real value for money [and] there has to be an alternative free route".

This, of course, begs the question of what is affordable. What is affordable to a Parnell multimillionaire politician is unlikely to be the same to the cleaner who has to drive across town from the more affordable suburbs to manicure his mansion.

National's intentions on tolling are part of the credibility gap in the party's plans for Auckland transport infrastructure.

With only two weeks of the election campaign left, Auckland voters need some detail to go with the rhetoric.

The $365 million Albany-Puhoi toll road is to open early next year with a toll expected to be $2. But even under "maximised" use conditions, the toll would pay only half the cost, and that over a 35-year period.

Using this model, what size toll would National consider "affordable" and economically effective, to fund the $1.89 billion Waterview motorway tunnels project? Then there's the $3 billion tunnel under the Waitemata Harbour, which North Shore National MP Wayne Mapp clamours for with talk of $6 return tolls.

A year ago, Mr Key told the Road Transport Forum conference that "National is not averse to using tolls on occasion to help pay for major roading projects, particularly where there is private sector involvement in financing".

But he is yet to spell out details. As the victims of the Labour Government's Alpurt tolling experiment, Aucklanders deserve to know what, if any, further tolling experiments National has up its sleeve for us.

In the back of many minds is National's poor record of transport funding in Auckland in the 1990s. Between November 1993 and November 1999, when Mr Williamson was Transport Minister for all but one year, only 25 per cent of Transit NZ's money was spent north of Pukekohe, despite just under 40 per cent of the population living here.

Urban Auckland was short-changed around $50 million a year over that period, to subsidise extra lanes of tarmac through National's rural voter heartland.

To hear Mr Key on the election trail this week dangling the carrot of $790 million of extra highway building for Hamilton is a reminder of those bad old pork-barrel days.

The other area of fuzziness is public transport, and in particular, the on-going funding of the electrification of the Auckland commuter network and the proposed line to the airport.

National has expressed opposition to the 10c--a-litre regional fuel tax being levied on Aucklanders to fund local transport projects, but has come up with no alternative. If they have one, I'd be as keen to see the tax go as anyone. Should we read their silence on this as ominous or not?

What also is their attitude to the proposed underground inner-city loop?

Battlers for electrification recall how Sir Dove-Myer Robinson's earlier rapid rail network got the green light from the Kirk Labour Government in 1975, only to be thrown out in 1976 by the incoming National Government of Robert Muldoon.

Mr Key is too young to remember such things, but there are many who do. They worry National will revert to type. As long as Mr Key remains mum on these details, so do I.