In my county, the jail is overflowing that they had to let go of people with smaller charges like driving on a suspended license. Hitchhiking is illegal on freeways and some highways, definitely illegal on many freeway entrances (those are very difficult to hitch anyways, just ask for a ride from the gas station next to you). However, they don't have room for you in jail, they can ticket you for just about anything. Hell in Wenatchee, WA, it's "unlawful" to beg, juggle, have a reputation as a railer or a brawler, even profane and vulgar language is on that list of "unlawful" things.
Egh, I won't get any further into law. I always get pissed at how our rights are diminished to promote capitalism.