A private-car-based economy is indefinitely sustainable. That's not to say Internet shopping is going anywhere, but one has to be in to receive, and there's the issue of having to return goods if unsuitable. Private vehicles will simply use different power sources as time goes by. The public are unlikely to accept government destroying their freedom to go where they wish as they wish. But it does depend on the population controlling themselves re family size, and the government stopping population increase via immigration. There has to be room on the roads.