There are good reasons to be pessimistic about the prospects for major new public transport infrastructure investments in Australian cities. Governments across the country are reluctant to increase taxes or make further borrowings. Opposition Leader Tony Abbott says he won’t help fund urban public transport projects if he wins the September election. Since public transport recovers none of its capital costs and only around a third of its operating costs, it’s unlikely the private sector will be interested, either.

So it’s worth thinking about what might happen if key new city centre rail projects like the proposed Brisbane Cross River Rail or the Melbourne Metro did not go ahead.

The Melbourne Metro is estimated to cost in the region of $9 billion. The main rationale is that the existing rail system is close to capacity and won’t be able to support anticipated growth in travel to the CBD unless the new line is built. Much of that forecast patronage growth is premised on continuing vigorous jobs growth in the centre (this is an area that warrants scrutiny).

But if the new train lines weren’t built, would our trains soon be like those in Delhi with passengers hanging off the sides? Would the roads be gridlocked from 4am till 9pm? Would Victoria become an economic basket case (again)?

Here’s a possible scenario. In the short term, trains and roads would become even more congested, as it takes time for people to recognise things aren’t going to improve. But in due course people always adapt. People would accept the need for other changes to the system and even (reluctantly) acknowledge that some measure of discomfort and inconvenience would very likely be necessary. Employers would start to push harder on flexible working arrangements. Many workers and students would spread their arrival and departure times and do more work from home.

State and local governments would prioritise available funding to small-scale infrastructure projects that support cycling, buses and carpooling. The state government and the the train operator would seek to wring more capacity out of the system. The initial focus would be on initiatives like running longer trains, but as the lower-hanging fruit is consumed they would turn to less popular measures, like removing seats from carriages and changing operating procedures, e.g. fewer express services.

The emphasis in the capital works program would shift to (relatively) low-cost capacity improvements, such as improved track signalling. The pressure to find more capacity would lead to improved work practices by railway staff.

Train fares would be increased in peak periods to ration available seats. Some fare concessions no longer apply in peak periods. Parking fees in the centre would increase, too. A cordon-based congestion fee would be introduced in the inner city to manage the increase in driving.

These initiatives would “release” a surprisingly large increase in capacity. The downside is travellers would have to cop changes, not all of which would be universally popular.