It's certainly their right to drive slowly, but in Washington state it is not their right to delay others:
> Slow-moving vehicle to pull off roadway.
> On a two-lane highway where passing is unsafe because of traffic in the opposite direction or other conditions, a slow moving vehicle, behind which five or more vehicles are formed in a line, shall turn off the roadway wherever sufficient area for a safe turn-out exists, in order to permit the vehicles following to proceed. As used in this section a slow moving vehicle is one which is proceeding at a rate of speed less than the normal flow of traffic at the particular time and place.
Also Alaska (http://www.legis.state.ak.us/basis/statutes.asp#28.35.135)
Also Colorado (http://law.justia.com/codes/colorado/2016/title-42/regulatio...)
And Montana (http://leg.mt.gov/bills/mca/61/8/61-8-311.htm)
Seems like a common regulation in certain states, particularly those with a lot of mountain terrain. (It is often not feasible in any circumstance to pass on the left on a mountain road, so I can see why these regulations popped up.).
I'd love to do that. Unfortunately, even at a slow speed, it can be _challenging_ (to say the least) to detect a safe turnout area (e.g. in winding roads on the way to Tahoe) soon enough that one can actually use it.
Some roads have very handy marked turnouts that make this very easy, but many times there are Very Small locations that one could have used had one known about it ahead of time, or been moving (even slower) slowly enough to turn off right away. Many of these are not clear that they are large enough for one car until you're next to it, and often times you can't easily tell whether they are paved or not.
I hate to say this, but... slow down more if you see a potential candidate approaching.
I'll hate you for it right up until I see you pull aside, once I realize what's up you'll probably even get a courtesy wave!
In the story these comments refer to the driver had no real place to stop his truck and I believe he was justified in going slow on a rainy/slushy road in a heavy track on a decline.
If you are driving slowly you should be letting others pass you whenever possible. I'm actually quite amazed that you actually need laws for that (not that our drivers are better in any way, it is just common sense).
For most vehicles, on most roads, opportunities to allow others to pass safely appear with reasonable regularity. Despite this law, in my experience most slow drivers choose to entirely ignore those opportunities.
Many states have specific laws regarding this which may make that untrue depending on circumstances. Here's a good overview[1] so you can look at your state's specific laws and see which apply.
1: https://www.nolo.com/legal-encyclopedia/free-books/beat-tick...
I'm not usually one of the slow drivers and I do get annoyed at the slow drivers when I can't pass them but I will still keep my distance and avoid trolling them with horns, lights or otherwise. The road is for everyone and some will be slower than me and some will be faster.