I carry the little pamphlets from Digihitch around, but they're rarely actually useful. I've pulled them out and read hitching laws verbatim to cops and had the cops just say "nope, it's not true."
The local hitching laws are generally just whatever the cops want them to be.
Actually, there's a bunch of states it's illegal to hitch in. Nevada, Idaho, and Wyoming for starters, but there's a bunch more. Plus, each state has laws about where and when you can hitch. For example, in Oregon you can walk down the interstate with your thumb out. In Wyoming, you have to walk against traffic on any highway, and can't walk down the interstate at all.
In Minnesnowda, the statute was shown to me by a highway patrol, as HE Gave Me A RIDE!! It is against the law to "solicit a ride from a private vehicle". So i would like to believe that you could wave down an officer and ask for a ride! All Interstates are 'controlled-access' highways, meaning no bicycles, pedestrians and the like. Lucky for me, i was standing on Highway 61, which is a 'trunk' highway. And when i explained to him i need to report all contact with authorities to my PO, in regards to this lift, he explained he 'seen me walking on the side ov the road and offered me ride".