As much as Australia and the USA are big, most of the trips are very much under 30-50 km of distance, those are easily covered by intercity trains, and in cities mass transit is a much more efficient way to transport people inside of their borders. If there's need to go somewhere unpopulated in a large landmass where this system doesn't cover, I'm totally ok with cars, the issue comes from not having other options that reduce the car dependency.

Comparatively to the total population, in the USA, Canada or Australia very few people are using a car most of their time to cover large distances in swaths of undeveloped land, being a big place correlates to almost never going to the very far off unconnected places exactly because it's so far away and inconvenient.

Cars are required due to urban development policies and lack of passenger rail connecting cities, not because the place is big, in Australia most of the population live relatively close by [0].

[0] https://pbs.twimg.com/media/EW9YTD2XsAIFYNx?format=jpg&name=...

"It's a really big place" isn't the reason for many having cars in Australia, it's largely due to cities that sprawl beyond the reach and capacity of public transport, it's due to a love of long weekend trips outside cities, etc.

Smaller cars and better use of suburban space would go a long way to reducing Australian personal use of fossil fuels .. which is a relativel small part of the larger use of fossil fuels here.