In parts of California you are allowed to ride on the freeway shoulder. AFAIK it’s only legal when there is no reasonable alternative.

I’ve done it a few times — it’s not ideal, but it’s not horrible, mostly because you don’t cross on/off ramps (it’s just from one exit to the next). In my case I did it because the multi-use path I was planning on using was temporarily closed.

I have been on a different ride where I crossed on/off ramps (I should have taken a different route!), and that really sucked.