Though Gov. Patrick didn’t mention the idea in his prepared remarks at today’s press conference, Transportation Secretary Jim Aloisi told Blue Mass Group that the administration plans to try out a VMT (“vehicle miles traveled”) tax as an alternative to a gas tax. The rationale is that a tax on distances traveled is more stable, in the long run, than a tax tied to fuel consumption. That is, even if the gas tax automatically rises with inflation, as Patrick proposes, revenue would decline sharply as people switch to more fuel-efficient cars. (The gas tax is arguably another “sin tax” in the sense that more bad behavior — smoking, drinking, gambling, and driving Hummers to convenience stores — means more money for the government.)

Ezra Klein agrees, calling the VMT “less galling for taxpayers” than a gas levy (even if it’s more frightening to some civil libertarians). But Matt Ygelsias calls the idea “off-base,” and a poor substitute for a gas tax or a congestion tax (and everyone knows how popular congestion taxes are):

When it comes to pricing driving-related activities, it makes sense to charge people from things that actually impose costs on others—burning gasoline, and taking up space on crowded roads—not the mere act of driving.

A guy who drives an SUV along a 25-mile stretch of the Beltway at peak morning rush hour is imposing a lot more negative externalities on his fellow citizens than is a guy driving a Prius 50 miles in the middle of the night on the outskirts of Albuquerque.

Aliosi did tell Blue Mass Group that a VMT pilot program would include anti-congestion measures, such as “peak pricing,” which would indeed address those negative externalities. Of course, that would also make the VMT plan more complex and would require the government to collect more data on driving habits (noting odometer changes wouldn’t be sufficient), so it would probably attract more political opposition.