I first posted this under the Riverlea and Mt Barker thread - maybe here is more useful
It is worth restating that to be warranted, fixed track transport requires sufficient demand to be focussed on nodes, both at the ends and at a few locations along the route.
It is highly likely that an origin and destination survey of movements originating in the greater Mt Barker area would reveal that a relatively low percentage of trips end at the city or other locations adjacent to the route through the Unley, Mitcham, Blackwood, etc. On the contrary, I would suspect that it would show the majority of trip destinations were spread across the greater metro area to the south, west and north. These latter trips are and will remain, under current conditions, the domain of private transport.
The likelihood of significant increases in employment in the CBD and/or along the length of the current line through metro sufficient to justify a fixed rail solution Adelaide would be low.
It is also worthwhile considering there are changes in the charging and payment structures for road based transport already being considered and, in some cases, proposed.
The revenue stream for road transport is reliant on a fixed yearly charge (eg, registration and insurance) and a variable charge based on distance travelled (eg, taxes and levies on fuel). The introduction of EVs with the associated loss of variable revenue will demand some form of replacement "pay as you consume" system. To be efficient and effective, this will need to be automated. At the same time, it is highly likely that this would be combined with a time and place levy, that is, a variable peak congestion charge incorporating day, time and place.
Overall, this system could be structured in a way that the "average motorist" would pay no more or less than currently. The big difference would be that payment would be at the time of consumption.
The result could well be that as a society we would end up travelling less, thus reducing the consumption of resources, reducing road trauma, reducing time spent travelling and so on. Surprisingly, we could reduce mobility and increase.accessibility.