I wondered about this myself, but I do see potential long-term effects of a purely gas-tax based system. Even electric vehicles contribute wear and tear to the

I wondered about this myself, but I do see potential long-term effects of a purely gas-tax based system. Even electric vehicles contribute wear and tear to the road system though they don't contribute emissions. The need for maintenance doesn't stop just because cars would be non-gasoline based. Eventually we will need to acknowledge this point from a purely pragmatic stance. Encouraging high-efficiency vehicles via a gas tax is a reasonable incentive now but it's not sustainable. I suspect that the eventual system will bear a resemblance to the one in use for long-haul trucking, where operators keep a detailed log of how many miles they drive in each state as well as loaded weight. GPS is one way to facilitate such a system.