Queensland voters are likely to face a flood of spending promises with unverifiable benefits before they head for the polls on January 31

The problem with cost benefit analyses of major projects, from a politician’s point of view, is they don’t include the political benefits of donning a hard-hat during an election campaign and promising a huge new whatever-it-is with lots of (possible) jobs.

This may be why politicians are usually far keener on cost benefit analyses in theory than they are in practice.

The problem with not having publicly available cost benefit analyses from a voter’s point of view is that we have no way of checking whether our money is being well spent on the whatever-it-is, or whether we are just being conned into thinking that the nice politician in the hard-hat has an excellent plan for jobs and the economy.

I mention this because the voters of Queensland – if they aren’t preoccupied with the cricket or summer reading or back-to-school book lists – are likely to face a flood of spending promises with unverifiable benefits before they vote on 31 January.

The Queensland government is, for example, promising hundreds of millions of dollars of taxpayers money in a desperate bid to get the $16.5bn Carmichael coalmine off the ground.

There are, of course, enormous environmental concerns about the mine – both its immediate impact and the wisdom of a mine slated to export 10bn tonnes of coal over its 90-year lifetime when yet another report warns that more than 80% of the world’s current coal reserves must remain in the ground to avoid dangerous climate change.

But even heaving all those problems off to one side and looking at the project only in economic terms, it is very hard to calculate whether the economic benefits justify the subsidies and sweeteners being flung at it to convince Indian proponents Adani to proceed.

Initially, as the “first mover” of all the possible mines on the giant Galilee coalfields, Adani was offered an open ended royalty holiday. A spokeswoman for the deputy Queensland premier, Jeff Seeney, said this offer had now been replaced by the offer of the government taking a minority stake in a 380km railway line to bring the coal to the Abbot Point port. The state government has never said how much this could be, but an Indian report said the government had offered to pay $455mn.

In addition, taxpayers would fund the construction of a facility in the Caley Valley wetlands to deposit sediment dredged in the construction of a new port to export the coal. The cost of this is also unknown – the state government says “commercial negotiations” can’t start until the new disposal plan is considered by federal environment minister Greg Hunt – and it is possible there would also be an ongoing cost for taxpayers for onshore dumping.

The expenditure of unknown hundreds of millions of dollars is justified, the state says, because of the benefit of the jobs and royalty revenue the mine would create. Adani’s advertising campaign claims 10,000 jobs will created, but elsewhere it talks about 5,000 construction jobs and then 3,500 permanent positions. And claims about the royalties it might pay are equally variable – the company talks about $22bn over 35 years and $6bn in the first decade of operation but this is based on disputed estimates of a recovering coal price.

And the hundreds of millions of state taxpayers dollars are all coming from the effective sale of other taxpayer owned assets. Queensland is proposing to offer long-term leases of ports, water pipelines and electricity transmission and distribution businesses to raise an “estimated” $37bn, but since the scoping studies won’t be released until after the election, this estimate can’t be checked.

And in any event, on his second day of campaigning Premier Campbell Newman said he wouldn’t go ahead with leasing assets if he didn’t think he’d get good value – which left things a little bit up in the air.

Whether or not $37bn is the amount, and whether or not it happens, the government is promising $8.6bn of it (bolstered by the bonuses paid under the federal government’s asset recycling plan) will be showered upon the Queensland public, much of it in election promises in coming weeks – possibly for the coal infrastructure and also for road and rail projects.

Since most of these commitments have been made without detailed public cost benefit analyses, voters will have to take the Queensland government on trust that they are good things to spend money on.

That’s pretty much what federal voters were asked to do too, when Tony Abbott pledged $3bn for the East West link road in Melbourne, without any public business plan, and what the former Victorian government asked voters to do when it made East West Link a centrepiece of its election campaign. When the cost-benefit analysis was finally released – after the Coalition lost the state election – it turned out to have a benefit of 47c for every public dollar outlayed.

That wouldn’t have come as a surprise to the Productivity Commission which – in a report last year commissioned by the Abbott government – explicitly warned governments against getting locked into lavish election spending promises before doing detailed analyses.

“The norm in major projects is that the announcement precedes the detailed planning … There are numerous examples of poor value for money arising from inadequate project selection, potentially costing Australia billions of dollars,” it said.

“Properly conducted cost benefit studies of large projects, and their disclosure to the public, is an important starting point for guiding project selection and improving the transparency of decision making

“All governments should commit to subjecting all public infrastructure investment proposals above $50 million to rigorous cost–benefit analyses that are publicly released and made available for due diligence by bidders. In general, analyses should be done prior to projects being announced. If a project is announced before analysis is done, for example, in the lead-up to an election, this should be conditional on the findings of a subsequent analysis.”

The productivity commission doesn’t seem to rate the political value of big-spending hard-hatted election announcements either. Campbell Newman is hoping Queensland voters will.