Surveys show Volt owners average about 66% of miles on electric; often because they take more advantage of public charging than BEV owners do. (Which is great; the Volt is a great solution for single-car families, or people without reliable access to charging. I'm just confused by the Volt owners that do 99% of their miles on electric - why didn't they buy a cheaper BEV that has more range if they never use the engine?).
Bringing it back to WA topics, the Volt has proportionately lower sales here than BEVs do because the sales tax waiver only applies to BEVs. (This is complicated by the fact that the i3 REX counts as a BEV). Although this may be moot come July 1 when the sales tax waiver expires (see post 5 above). It will be interesting to see how sales rates change if that happens.
By the time the Model III is available, we might not only be missing the state sales tax waiver, but Tesla may no longer be eligible for the federal tax credit either. But if Tesla really hits their targets with the Model III, I don't think it's an issue - by then people will be so familiar with Tesla, and the Supercharger network should be nicely built out, that I think they will be able to sell all they can build regardless of credits. (Though they may sell more of them in states that still offer credits, improving that state's economy and environment rather than ours).
There are enough Tesla in WA already that I think the market will be pretty well seeded for Model III sales. We've got lots of engineers, pilots and doctors here (who seem to be early adopters for this type of technology). We've got good salaries so people can afford new cars. And we've got little polluting industry so most air and carbon pollution comes from gas vehicles; at the same time we've got one of the cleanest grids so EVs can do more to reduce pollution here than in most other states. Our higher-than-average gas prices and lower-than-average electricity prices help too. Due to its unique geography, the biggest issue for Puget Sound water quality is oil and gas runoff, so switching to EVs is important for that too.
Another geographical advantage is that the main traffic corridor is I-5 (sandwiched between water and mountains), with a few smaller ones going East - that makes it relatively easy to cover the main traffic corridors with DC chargers.
I think WA's long-term EV adoption will be good, and the Model III will do very well here. And personally, I'm very eager to see an EV that is smaller than the Model S, more practical than the Roadster, and cheaper than both. Too bad we have to wait until next year to get any details on the Model III.