It seemed that my mother in law, because the state law did not require her to be buckled up if she was a back seat passenger, wouldn't buckle up. My brother in law decided, rather quickly, that he wouldn't buckle up, either.
On the other hand, I am strict about any back seat passengers being belted up. My son, if he hadn't been buckled in, would almost have certainly have died in a car crash when he was young. I remember how obsessed the emergency room crew seemed to be about if he had been buckled in. The bruises and outline of the shoulder belt proved he had been buckled in.
In the same crash, my husband and I were also buckled in, and we only suffered bruises.
It was a little bit of a struggle to get my brother in law to accept the back seat belting in, but we insist on it (since my mother in law always rides in the front now, her belting in is not an issue as she obeys the law.) It's worth the struggle, now that videos show what happens if a back seat passenger isn't belted in.
Oh, about the seat belt laws - each state in the United States has its own laws.
Remember the old jingle? Buckle up for safety. Buckle up. Show the world you care. Even if you have autism.