Earlier quoted context omitted.
Many countries are similarly bad, yet still have cars; Singapore and Hong Kong for example, which are otherwise libertarian paradises. They tend to have excellent public transportation, however. There are also still cars in Denmark (no problem seeing them when I visited Aarhus), just not as many as in the states.
The thing is - 100% tax on cars is libertarian. You charge car owners something closer to the costs they cause to society. Compare that to the USA where we heavily subsidize car ownership.
Also, a $50,000 car does not have double the societal impact as a $25,000 car (which could be larger and less fuel efficient). Progressive taxes aren't a very libertarian construct.