There's several pop-up communities at Freeway intersections here in San Diego .
The one at the 94 west to 5 northbound Caltrans large maintenance "triangle" gets cleared out every three months or so; within a week, the regulars start setting back up. I'm pretty sure there's some Caltrans that warn them when a sweep goes through
The regulars are a mix of around three five couples of elderly and vets with pets (after four or five years of using the onramp, I recognize the tents and the dogs); they're pretty good about policing the area and bagging up after themselves, but still - it's a dangerous location.
If there's a large safe camping area nearby with maintained facilities offered to them, I'm sure they'd rather set up there than figuratively in the freeway.
But I guess that's too humane or indulgent for throwaway people.