Speaking of congestion charges, here's a related idea making the rounds. As I mentioned last week, insurance companies are starting to think about charging drivers for each mile they drive. But now it turns out that state governments may beat them to the punch: The AP reports that Oregon has established a pilot program for monitoring vehicle mileage remotely, equipping 300 cars with GPS devices that track mileage, location, and the time of day that the car is used. Oregon is just one of several states exploring ways to track vehicle mileage, with the goal of eventually replacing gas taxes with a per-mile road-use tax. The reasoning here is that, in the future, people will be driving cars that use little or no gasoline, which would leave states in the lurch if they don't figure out some sort of replacement for the gas tax.

It's an idea that strikes me as a bit premature. Sure, in the long run, we'll all be driving electric cars or plug-in hybrids, at which point it would make sense to have some sort of mileage-based tax that states could levy to pay for road maintenance. In the near term, though, if less driving and a shift toward more fuel-efficient vehicles do start putting a squeeze on a state's road budget, then the easiest and most environmentally sound way to make up the shortfall would be to simply increase the gas tax.

But if they ever do go into effect, GPS-enabled per-mile road taxes could be a nifty way to make congestion pricing a reality over large swaths of the United States (perhaps even in New York City, where Mayor Bloomberg recently tried and failed to implement it). As the federal Transportation Review Board has pointed out, it would be relatively simple to charge drivers different per-mile tax rates depending on which roads they used and when they used them. (There would be obvious privacy concerns to address, though these problems might not be all that different from the ones inherent to the EZ Pass or other electronic toll-collecting systems.) Differential pricing would be an easy way to discourage drivers from using roads during peak times, leading to fewer accidents, less wasted gas, and a lot less wasted time during rush-hour commutes.

--Rob Inglis