Psc:
You're pretty much right on, except it's a fed law, and trucks & combinations may use the 2 right lanes, only. Hill climbing lanes, exit ramps, HOV lanes, etc...dont count. (Dont get caught in a HOV lane in a big rig, though.)
I dont believe Thurston Co is trying to get away w/ anything, though, there are localized restrictions which may be applied wherever DOT feels a specific need. So that RH lane thing is only for (probably) that particular hill grade.
The one thing very important, however, is that little combos are restricted to the truck & trailer speed limit... I see soo many cars w/ boats & campers zipping along at 70,(+ often) not even realizing its worth a real fat tix., and not aware of the public hazard they're bringing to the road... They dont realize how much more stopping distance they need, or how quick they can lose it if they blow a tire, or whatever.
I drove over the road big rig for as coupla years, and even tho I dont do it any more, the education I got was immeasurable. I saw some really stupid stuff out there, and was constantly amazed at how unwilling people were to accept responsibility for their lack of judgement...
Well, nuff said. Be safe getting there and back. Even if there are fish there to be caught, its just not worth a tix or accident.
'Head hunter