“with GPS they can track how many miles you drive and where you go etc”
Yes, that’s the plan.
If you drive in another state, they don’t charge you for it, but they can report that mileage to that state, so you can be billed for that, too.
After a while, when the mileage tax doesn’t solve the revenue shortfall, they will gradually bring back the fuel taxes.
They can/will also have a highway tax at each annual registration. This one would be highest for electric vehicles.
Oregon’s program:
http://roadchargeoregon.org/frequently-asked-questions/#FAQtax
http://roadchargeoregon.org/frequently-asked-questions-2013-pilot/
You will be charged by California if you are a resident there for all the mileage you have driven.
IF you are retired & drive to visit others around the country, California will collect that tax per mile on top of the state gas taxes you paid in all the states you visited.
Seems like double jeopardy to me.