For an "infrastructure prime minister", Tony Abbott's efforts have been pathetic, especially since paying back borrowed money has never been quicker and he could do it all without hurting the budget bottom line, writes Alan Kohler.

Tuesday's budget was pretty lame, that's for sure, dealing with neither the weak economy nor the structural deficit, mainly shuffling a few billion dollars from one set of welfare recipients to another.

The Government seems to have been paralysed by the impossibility of tackling both the structural deficit and the weak economy.

Best to do nothing at all and leave both jobs to the Reserve Bank. That is, assume that monetary policy fixes the economy and that brings down the deficit.

Big assumption, and anyway you can do both. Here's how.

First, a look at the problem. The 2015 budget states:

The 2015 IGR shows that structural savings measures already implemented by the Government are projected to make a significant contribution towards achieving fiscal sustainability over the longer term.

Yes, except that much of the savings are stuck in the Senate and there is no sign that they will become unstuck, including measures that the Government has not yet quietly strangled, such as the cuts to Family Tax Benefit B and the higher education reforms.

And remember the $80 billion in cuts in payments to the states over 10 years? They're still there - totally unmentioned this year, but counted.

But by far the biggest problem for the budget is revealed in this remarkable graph deep in the budget papers, in a box entitled "Box 2.1: Trends in social security and welfare spending":

A footnote explains that: "The growth in the social security and welfare function mainly reflects the implementation of the National Disability Insurance Scheme."

As Prime Minister, Julia Gillard had two big ticket spending items: the NDIS and the Gonski education funding reforms. Tony Abbott has ditched Gonski and kept the NDIS.

But the NDIS is about to swamp the budget with a total of $20 billion over the next three years, in extra "real" expenditure - that is, spending over and above the inflation rate.

Box 2.1 goes on to provide another way to look at it. In the 2014 budget, the increase in social security spending over the forward estimates (four years) without the NDIS is shown to be 2 per cent per annum; with the NDIS, it is 8 per cent.

This year it's 2 per cent per annum without the NDIS, and 12.3 per cent with the NDIS - a difference of 10.3 per cent per year.

The result is that total government expenses compound at 3.7 per cent next financial, 4.2 per cent in the following two years, and then 5.9 per cent in 2018-19. This is a very frightening compound growth, and there is no sign that Treasury is preparing for it.

Specifically, the budget emergency that the Government needs to prepare for, but hasn't, is paying for the plan to support Australia's disabled people.

As a result, the size of government will stay above 25 per cent of GDP through the forward estimates - much more than the 23.1 per cent to which the Labor government got it down to in 2007-08, before the GFC.

In his budget speech, Treasurer Joe Hockey said:

...over the same period (the four year forward estimates) we are reducing the size of government as a share of the economy.

No they're not. Well, OK, it will be down from 25.9 to 25.3 per cent of GDP.

By the way, those figures are not necessarily bad - in fact, Australia's government sector is among the smallest as a share of GDP in the world. It's just that tax receipts are insufficient to pay for it, resulting in the structural deficit (not mentioned this year).

Joe Hockey also said in his budget speech: "We cannot tax our way to prosperity."

Well, actually, tax receipts are up to 24 per cent of GDP in this budget, compared to an average of 22.4 per cent during the Labor Government.

The dirty little secret of this budget is fiscal drag - where wage inflation moves taxpayers into higher brackets. That's why the deficit is falling - not because of spending cuts.

Australia also has an infrastructure deficit, as well as a weak domestic economy, partly caused by the poor state of the nation's infrastructure. This chart comes from CBA Economics:

To get Australia's economic infrastructure stock back to the 65 per cent of GDP that it was 30 years ago would require spending of $150bn.

Included in the 2015 budget - and the only thing actually announced by the Treasurer, as opposed to being leaked or pre-announced by Scott Morrison - is a $5bn Northern Australia Infrastructure Facility "that will be available" for projects like ports, railways, pipeline and electricity generation.

Available to whom? When? Which projects? And by the way, the Treasurer's budget speech might say it's $5bn, but the detail of the budget papers shows that it's actually $388.3 million per year, which suggests that the lump of cash will actually be dribbled out over 12 years.

There's also a $1bn "National Stronger Regions Fund" that already started dispensing money last year, $100m set aside to improve roads to get cattle to market, and $263m for Tasmanian stuff.

As for any serious effort to respond to RBA governor Glenn Stevens' recent call for "investment in quality public infrastructure" or to take advantage of the record low interest rates for public borrowing, there is none.

In fact, the main reference to infrastructure in this budget involves the removal from it of the $1.5bn set aside for Victoria's East-West Link - it reduces Commonwealth spending by $300m this year, $600m next year and $500m in 2018-19.

That's the money that's being recycled into the North Australian Fund. That's right: the "vision for the north" is simply some of the money that's being taken off the Victorian Government because it's not building the East-West Link and is building another road instead, in accordance with its election mandate.

In his election policy in 2013, Tony Abbott said: "If elected, I want to be known as an infrastructure prime minister. But I won't be all talk and no action like Kevin Rudd."

Yes you will. The Abbott Government's efforts on infrastructure have been truly pathetic, especially with the 10-year bond rate at 3 per cent, which means the payback on any public infrastructure that is paid for by Government borrowing is the shortest it has ever been.

And, by the way, investment in infrastructure does not even have to worsen the deficit, structural or otherwise.

There is a table on page 3-25 of the budget papers, which is there every year, that reconciles the "underlying cash balance" - that's the $35.1bn number that the Government has announced as next year's deficit - with what's called the "headline cash balance".

The headline cash balance for 2015-16 is $44.76bn, $11.6bn more than the underlying cash balance (I would have thought the terms "headline" and "underlying" should be the other way round, but that's another matter).

The difference is primarily student loans, $7.9bn, and the NBN investment, $7.8bn, offset by something called "residential mortgage backed securities" of $4bn (I don't know what that's about) and Future Fund earnings of $3.2bn.

In other words, there is a bunch of things that are what a company would call "off balance sheet", or "abnormal items" - not included in the profit and loss account. The Government calls them "net cash flows from investments in financial assets for policy purposes".

Over the forward estimates (the five years to 2018-19) these things add up to $68.2bn, dominated by $49bn in student loans and $21bn for the NBN, although I'm not sure how you can call the NBN a "financial asset". If that's a financial asset, then so is a road.

Would it be too much to ask to add, say, $10bn for public transport to that tucked away figure? Frankly, I can't see why you wouldn't add $100bn to it and really bring the nation's infrastructure up to scratch - and really be known as the "infrastructure PM".

By putting the NBN spending into this "headline cash balance" account instead of the "underlying cash balance" that's announced as the deficit, the Government is clearly signalling that that is where infrastructure spending belongs - out of the budget, as an investment.

But apparently that would be too visionary.

Alan Kohler is a finance presenter on ABC News. He tweets at @alankohler.