Mileage tax for highway funds? What's the real motivation?

Introduce a mileage tax to make up for lost revenue caused by fuel-efficient drivers paying less in gas taxes? Your tax dollars are hard at work as state and federal officials ponder that very issue, according to today's Washington Post.

The article outlines a few of the debates that will rage at our -- quite literal -- expense:

• Invasion of privacy (not that any of us with E-Z Pay or similar transponders have paid much attention to that until now)
• More taxes in general (do we really think the gas tax will be supplanted?)
• Should more efficient vehicles get a tax break (or the reverse, i.e. The Hummer Tax)?

My personal objection, though, is rooted in the double-speak regarding the motivation. What is guiding our transportation policy these days? Are we striving to reduce greenhouse gases, or are we motivated merely by the shortfall in federal highway system's maintenance budget?

One of the points made in the article is fewer people are driving these days, and the drivers that remain drive more fuel efficient cars. Car makers, albeit influenced by government regulation, are in turn striving to build and sell more fuel efficient cars -- some that could reach 100- and 200-miles per gallon efficiency.

So we will have the ability to drive farther and more efficiently, but will get penalized for that distance with a mileage tax?

Here's an idea. Want to keep us off the road? Let the highway system go to seed.

Don't use proceeds from a mileage tax for highway upkeep. Use the money to fund more mass transit projects, like the Urban Ring or connecting North and South stations. Extend commuter rail to more destinations. Build more bikeways. Motivate people to stay off the roads.

Granted, I'm the last one to heed in this debate. I commute 600 miles round trip twice a month, and there's very little that could be done in the near future to provide an alternative or prevent the trip altogether. But if there's going to be a mileage tax, I'd feel a lot better supporting it if I knew it was improving long-term transportation options.