Transport Minister Gerry Brownlee is refusing to rule out nationwide petrol tax increases to help pay for a $12 billion shortfall in funding for major transport projects in Auckland.



He is also hinting that rail users may help fund a greater share of the cost of public transport or have passenger subsidies eased as public transport usage rises.



Yesterday a report commissioned by the Auckland Council on future transport funding concluded that one form or other of road tolling was inevitable to make up the $12 billion gab between the expected cost of committed projects and allocated funding.



Brownlee has already ruled out a series of options raised in the report, including a regional fuel tax, congestion charging and tolling on existing motorways.



However he was not ruling out an increase in nationwide fuel excise, on top of the three years of 3c/litre increases committed for 2013-2015.



''No one can do that [rule out excise increases],'' Brownlee told Radio New Zealand this morning.



''We've made it very clear that we think that's what's necessary and these things have come in annually or bi-annually for quite a long period of time,'' he said, adding fuel prices were ''quite confused'' by discounting.

Brownlee played down the significance of the apparent shortfall because the projects would be delivered over an extremely long timeline, with uncertainty over the start date of key projects.



''The gap is somewhat notional'' and was derived using assumptions over rail subsidies and public transport patronage calculations.



''But when you're looking at it over such a long horizon I think you've got to be careful that you don't knee jerk into positions that are very costly in the long term.''



Significant analysis would need to be conducted to work out funding options, but Brownlee signalled that be believed public transport could pay a larger share of the costs of the projects.



''At the moment there's quite a heavy subsidy on the rail. If you're taking a trip from West Auckland into Britomart, at the present the passenger subsidy is approaching $10,'' Brownlee said.



''So there's a lot of opportunity there as you see the new services coming on with a much more frequent interval and the possibility of those trains filling up, there's quite a big revenue stream that could potentially come from public transport.''