I know WA has this law too. I think BC has it too, it's just never enforced, but there was word that enforcement will be increased.
My mini rant on this is people that think doing the speed limit in the fast lane is fine, even if you've backed up traffic. If someone wants to go beyond the speed limit, it's not another drivers job to block them and play paasive police officer. Just move to the right and mind your own business.
When I was in the UK, everyone follows the "stay left except to pass" rule really well. There were times when I'd be on an empty motorway doing 80 in the middle lane, and someone is coming up on me doing 90 in the slow lane. Rather than pass in the slow lane, they'll go around to the fast lane to pass, then return back across to the slow lane. It's as if they've been trained on it so well. Why can't this happen here?