I was under the impression these laws have become much more common over the past decade or two when they were a rarity beforehand. My home state (MN) for example didn’t have one for the first 15 years or so of me driving. Much to my chagrin after I learned about how much better life can be by spending time in a state (KY) where it was strictly enforced by both social convention and law enforcement.

Surprisingly it seems to even be moderately enforced these days even in Minnesota, which I’d have bet money on never happening since it’s a state pastime to play passive aggressive traffic cop for many.

https://www.reddit.com/r/coolguides/comments/1fuw97s/a_cool_...

Perhaps not the most trusted source on the matter, but at a glance it seems more or less the vast majority of states have laws that effectively “ban” slow moving traffic in the left lane from impeding traffic. Enforcement I’m sure will be all over the map - likely down to even a county level within individual states.

While I do wish all states were “purple” or above in that map, the situation seems largely up to how state patrol and other agencies want to enforce it.

I’ve seen it enforced now with my own two eyes in KY, WI, MN, and IL.