Those porous borders around the Northwest are super-sensitive to legislation, maybe more so than anywhere else in the states. Subtle distinctions can have a big effect on interstate traffic.
As a student at the University of Idaho at Moscow, I would watch from my form window toward the west, to the point where Idaho became Washington, and where cars slipped between the two on Highway 8. Early in the evening, especially on Friday and Saturday nights, I would watch the steady stream of white lights from Pullman - heavy traffic to Moscow. After midright, the lights would turn red, traffic headed back to Pullman, home of Washington State University. The reason? Idaho's drinking age then was 19, to Washington's 21.
Change now drinking to smoking, as reports now point to smokers flocking across the border from Washington - where almost all public places, including bars, are required to be smoke-free - to Idaho, where the rules aren't quite so strict. That's ironic, since Idaho did toughen its statewide smoking rules considerably just a couple of years back.
So expect to see some altered traffic flows on the Lewiston-Clarkston, Pullman-Moscow and Spokane-Coeur d'Alene lines. The legal marketplace at work.