Back in 2015, when former prime minister Tony Abbott stuck a shovel in the ground to celebrate dirt churning on Sydney’s WestConnex motorway, he said motorists would be “singing in their cars” when the 33-kilometre toll road was finished.

“They will be rejoicing, they will be singing in their cars, frankly, because their cars will be moving,” said Mr Abbott, who committed $1.5 billion for the project in 2013 – before WestConnex’s business case had been publicly published or reviewed.