Infrastructure Australia has low confidence the Allan government can build the first stage of its Suburban Rail Loop pet project for the current price tag of $34.5 billion and says it needs exit strategies in case the project cannot be delivered at all.

The federal government’s adviser on big projects said the Albanese government should tip no further money into SRL East until an updated cost estimate was completed and details provided that show how Victoria’s plan to fund a third of the work via a process known as value capture would work.