My employer offers a subsidy for using mass transportation, but i doubt it equates to what they pay for in parking.

gas taxes, in the US, are priced per gallon of gas (not as a percentage of sale like sales tax). Theoretically this already punishes gas guzzlers and high-volume drivers more than those of us driving less distance or more economical car models.

The problem is the taxes aren't high enough to affect drivers decisions.

The proposed solution of charging per mile driven has been presented in Oregon. Their solution was mandatory GPS on all cars that tracked the miles. I doubt the EFF would approve such measures.