But politicians are not supposed to spend public money to promote their private interest, including their private political advantage. Avoiding such conflicts of interest would be more straightforward if the federal government stuck to its national role, and did its due diligence before spending public money.

Pork-barrelling happens year-round, but there’s more of it during election campaigns. And the amount promised during election campaigns is on the rise, jumping from one year’s worth of federal transport spending promised in the 2016 federal campaign to seven years’ worth in the 2019 campaign.

But election promises are often particularly poorly thought-through. In the 2019 campaign, only one of the Coalition’s 71 transport promises valued at $100m or more had a business case approved by Infrastructure Australia; that promise was $390m towards the duplication of the North Coast Line on the Sunshine Coast. The 71 projects also included $800m for the Gateway Motorway Extension in Brisbane, and $500m for a Princes Highway upgrade on the south coast of NSW.

For Labor, only two transport promises of a total of 61 had a business case approved by Infrastructure Australia – the same $390m for the Sunshine Coast’s North Coast Line as the Coalition promised, and $2bn towards the Melbourne Metro rail tunnel. Among the 61 without an Infrastructure Australia-approved business case were $3bn for Sydney Metro West, $2.7bn for Adelaide’s North South Corridor, and $2.2bn for Brisbane’s Cross River Rail.

Much of what the government spends on transport projects is outside the role that it has agreed with the states. The government is supposed to focus on nationally significant infrastructure in the National Land Transport Network, while locally important roads and rail are the responsibility of state and local governments.

That hasn’t stopped successive federal governments from funding nearly 800 roundabouts, carparks, and overpasses since 2009. So clear is it that the federal government has no business in small local projects that more of the commuter carparks promised by the Morrison government before the 2019 election have been cancelled than have been built. Some lacked feasible site or design options, some lacked the support of the state or relevant local government, and some faced community opposition. Eleven per cent of the Urban Congestion Fund has been allocated to projects that aren’t even within the capital city boundaries.

Federal pork-barrelling on transport projects favours electorally important states. Queensland and NSW, where federal elections tend to be won and lost, consistently receive more, and Victoria less, than can be explained by population, population growth, size of the road network, share of passenger or freight travel, or what it actually costs the state government to run the transport system.

The government compounds this inequity by funnelling much more discretionary transport funding to the most marginal seats, such as Lindsay in Sydney, Higgins in Melbourne, Moreton in Brisbane, Hasluck in Perth and Boothby in Adelaide. The average marginal urban seat received $83m from the Urban Congestion Fund; the average safe Coalition seat received $64m, while for safe Labor seats, it was $34m.

Funding modest-sized transport infrastructure doesn’t have to be so partisan. There’s barely any difference in what kind of electorates received money under the Black Spot and Roads to Recovery programs under both Labor and Coalition governments. The difference is that these programs have much more objective and transparent criteria.

But it will be partisan. Already we’ve had Labor out promising to run yet more studies on either faster rail or bullet trains down the east coast, and the Coalition promising to spend $678m on the Outback Highway between central Queensland and central Western Australia. Neither of these projects is on the National Land Transport Network, and neither has a business case approved by Infrastructure Australia.

Voters should demand better. Whichever party wins the 2022 federal election should strengthen the transport spending guardrails. The government, whether Coalition or Labor, should require a minister, before approving funding, to consider and publish Infrastructure Australia’s assessment of a project, including the business case, cost/benefit analysis, and ranking on national significance grounds.