I don’t know the Australian constitution or legal structure either, but as vehicle regulations are set by the feds thes states still need to deal with the repercussions. They could do nothing instead, but they have no power to reduce vehicle sizes. A better approach might be to get rid of parking requirements altogether. But, that’s more likely to be political suicide for the elected officials than to spur on a broader anti-car sentiment, especially given the rural nature of the state.