Comment: Super Fund should not be Auckland's slush fund

Is an unexpected white knight riding into Auckland, weaving through the chronic congestion of a city bursting at the seams?

The surprising news that the Superannuation Fund will cajole capital to build Phil Twyford's tram projects immediately raises the question of what else it can help pay for.

The Government savings scheme has already dipped its toes into infrastructure investments - about 2 per cent of the fund's $38 billion is in these sorts of projects around the world.

But it has yet to fund a big job like tram lines in this country with the bulk of the $5b it has invested here being either in timber assets or listed equities such as Metlifecare and Z Energy.

But there'll be no shortage of officials - right up to Auckland Mayor Phil Goff - who will be hoping the Super Fund gets a taste for more public projects.

New Zealand's largest city desperately needs more money as it struggles to accommodate the number of people who have flocked to it over the past few years.

So why shouldn't the vast amounts which the Super Fund has at its disposal be put to use in helping to get Auckland moving?

Because that's not its mandate - it has an obligation first and foremost to grow the money it manages to help pay for superannuation.

The country's population is getting older and the cost of servicing fortnightly pension payments is only going to balloon, particularly with a lack of political appetite to raise the retirement age.

By 2050, it's estimated that $76b a year will be needed to pay for super, compared to $13b in 2017.

Which means that the Super Fund needs to remain completely focused on getting the most bang for its buck, having averaged returns of more than 10 per cent per year since it began investing.

It no doubt has run the numbers and thinks it can get a decent amount back from Twyford's trams but should refuse any push for it to become the country's infrastructure cash cow.

Because while better roads, an inner city rail link and a waterfront village for the America's Cup all cost money, none of them will help pay for our retirement.