Of the $2.8 billion in new infrastructure commitments for the state, almost all benefit the marginal federal seat of Boothby, held by the Liberals by just 1.4 per cent, and the seat of Mayo, a former traditional Liberal stronghold now held by independent Rebekah Sharkie.

The lion’s share of the infrastructure funding will go to just one project, with 82 per cent of the spend earmarked for the Darlington to Anzac Highway section of the North South Corridor which will connect Boothby up to SA’s biggest-ever road project.

Even excluding the North South Corridor, most other new projects primarily benefit Boothby and the key Liberal election target of Mayo.

The second biggest project will see $200 million spent to fix up Marion Road bottlenecks at intersections with Anzac Highway and Cross Road on the northern edge of Boothby.

“The stretch of Marion Road that crosses the tramline and Cross Road is one of the worst bottlenecks in Adelaide,” said Finance Minister Simon Birmingham.

“The Morrison Government has heard the concerns of commuters, the RAA and businesses and is committing $200 million to save people time, money and frustrations.”

There is also $120 million for the Adelaide Hills Productivity and Road Safety Package, which primarily focused on road upgrades within the seat of Mayo.

Mayo also benefits from $60 million for the second stage of the South East Freeway Managed Motorways, and a further $16 million for upgrades of Main South Road along the Fleurieu Peninsula.

South Australia’s eight other federal seats, all considered relatively safe, largely miss out on the infrastructure spend.

There is $20 million for the Marion Road and Sir Donald Bradman Drive Intersection Upgrade, and a further $16.2 million for the Port Augusta to Perth Corridor Upgrade.

Another $60 million is earmarked for Targeted Investments to Improve National Supply Chain Resilience, which will go to unspecified projects around the state, while $50 million for the Rural Roads Package will include upgrades to the Horrocks Highway Corridor.

The Darlington to Anzac Highway section of the North South Corridor will also benefit the seats of Hindmarsh and Adelaide in addition to Boothby.

Virtually all of the infrastructure commitments in SA focused on roads, with nothing new offered for public transport or electric vehicles.

The RAA welcomed commitments to upgrade Marion Road and the Adelaide Hills Productivity and Road Safety Package, but noted that some key projects were overlooked.

“We’re disappointed there is no commitment to progress the duplication of the Augusta, Dukes and Sturt highways, which would support economic recovery and greatly improve road safety in regional areas,” said RAA safety and infrastructure senior manager Charles Mountain.

The emphasis on Coalition targets in SA mirrors national spending on marginal seats, with more than half of $6.4bn allocated to projects within a single electorate directed to marginal battlegrounds.

Prime Minister Scott Morrison on Monday denied that the budget’s infrastructure spending targeted marginal seats.

“It’s targeting the strength of our economy because that’s what Australians need,” he said.