A quote from this article, which also covers this trend across the US for replacing lost revenue from gas taxes:
The new year is only two weeks old, but we already have a candidate for one of the strangest public policy proposals of 2013. Virginia Governor Robert McDonnell has proposed eliminating the state’s 17-cent-per-gallon gas tax, increasing the state’s sales tax to 5.8 percent from 5 percent, and levying a new $100 annual charge on vehicles that run on alternative fuels. Meanwhile, in Washington State, electric vehicle owners are subject to a new law that requires them to pay a $100 annual registration fee. It seems somewhat perverse. [...] But these moves also highlight a new reality.
Also relates to Oregon thread: http://www.teslamotors.com/forum/forums/oregon-plans-introduce-tax-mileage