Why?

The more miles you drive, the more the driver pays. This is how the gas tax works. But, as in California, Texas is considering a per-mile transportation tax. The only good I see in it is an idea to charge drivers more during peak hours. But that alone is not worth discontinuing the "point of purchase" tax. Raise the gas tax, Texas (and you, too, California--and you, too, U.S. federal government), and witness more clearly the incentives of driving a more fuel-efficient vehicle. Replace the gas tax with a per-mile tax, and see the road's share of fuel hogs remain as high as today or even increase (and also take note of the use of expensive, high-tech, GPS-driven, possibly privacy-invading mileage counters when low technology will do). Use a mix of the gas tax and variable, demand-responsive per-mile taxes, and you have a system of network regulation and public funding that, however innovative, probably is not worth the heavy effort of implementation when compared with a system of higher gas taxes and variable tolls on key road links (the latter using common, existing technology).

In short, if Texas wants to update its consumption-based transportation funding model, a gas tax increase is all it really needs.