This is a horrible idea. It is just another trick the government will use to spy on you.

You filled your tank, you paid your gas tax, now the government should go away, and keep its oppressive nose out of your business. It is none of the their business were you drive with the gas you paid for.

Notice how the fallacious threat of global warming just gives the government another excuse to stick their nose in your business.

As with almost any government program, the devil is in the details. The specifics of how such a program would be implemented and what the goals would be will determine what effects it would have.

As Stephen Jaye pointed out, gasoline taxes have the effect of encouraging people to reduce their gasoline consumption (although not nearly as much as the high cost of oil last summer) by switching to more fuel efficient vehicles and driving less. A direct desirable effect of this is to reduce greenhouse gas emissions. Another effect, however, is that it reduces the amount of money available for road repair which also is the same pot of money the federal government uses for grants to improve cycling infrastructure.

With the growing popularity of plug-in hybrids and future vehicles that can make trips without ever turning on the internal combustion engine (or just bringing back the electric cars), the fuel tax revenue will decline even more while these drivers will have less incentive to drive less but will still be responsible for road wear and, depending on how the electricity is generated, greenhouse gases. Therefore, taxing by mile driven has great appeal and adds some fairness to the road construction and repair financing system.

I think there should be a combination of gas and per mile taxes. Furthermore, I think these fees should increase with the vehicle weight commensurate with the increased damage done by heavier vehicles. Lots of details need to be worked out not the least of which is how to get data about how far vehicles are driven. I don't like the idea of my car being equipped with a GPS device that records what roads I have been driving on since one can't ensure that information wouldn't be subpoenable. Besides, my vehicle already has a device which records its mileage. Many of the consumer items I buy come with an RFID tag that can be read by remote sensors to identify the package so why can't my car have a unique identifier tag and a device to transmit the odometer reading?

To the contrary, its a fantastic idea. As alternative fuels and fuel economic vehicle become more and more popular less and less gas will be sold. But a comparable amount of wear and tear on the roads and the cost to maintain the roads will continue to rise as long as people adopt driving as a necessary part of life.

The goal is to reduce driving at every stage because it is not a sustainable method of transportation, period. No matter what fuels we put into cars and what the roads are made of we will have to fight pollution and environmental waste. The best way to reduce driving is to tax the miles people drive, which acts as a disincentive for people to drive anywhere. Less people driving means less energy used to travel, means less pollution, means a better quality of life.

I think this is a terrible idea. With a tax on gas itself, less efficient cars pay a higher tax per mile, because they get higher mileage per gallon. These cars also tend to be responsible for a greater amount of ware and tare on the roads. Therefore, these cars should pay a higher tax per mile (as they do with a tax on gas), as they create a greater need for road repair. Switching to a tax on mileage would inadvertently subsidize gas guzzling vehicles- TERRIBLE IDEA.