When a tax on gasoline is political suicide but the necessity of the American transportation economy, elected and appointed officials are trying to come up with creative ways to encourage conservation. With hybrid car tax incentives, and permission to travel in the HOV lane and park free, lawmakers have become less creative.
In Oregon and California, officials are talking about imposing a tax on miles driven. GPS tracking would tax motorists who drive the most, and tax drivers based on time of day - just like your utility company. During rush hour, taxes would increase; at off hours, taxes would decrease.
A system of this scope would be exceptionally difficult to implement, and would be exceedingly unpopular. Few drivers are indifferent to taxes on consumption, but even fewer embrace the big brother feel of GPS monitoring.
Good luck getting re-elected.