A number of regulators and planners think the idea of charging motorists by the mile rather than multiple fixed fees and taxes is a good idea. Several states and a number of European countries are exploring the idea of establishing per-mile fees that would use GPS navigation systems to track how much a vehicle is driven. A fixed rate could be charged or the fee might be adjusted to reflect the fuel-efficiency of a vehicle, perhaps even when and where it was driven. As fuel prices soar, American motorists are driving less and there seem to be few options to recover lost highway revenues other than raising excise taxes or adopting an alternative system. Few people expect the pay-as-you-drive system to go away.