How do you know they drink on the way home, out of curiosity? Wouldn't think that was info they willingly share. It is pretty amazing how quickly social (and legal, obvi) standards change. My wife remembers her dad drinking beer during long road trips in 80s. My grandfather used to own a newspaper business in a small town and all my aunts/uncles remember him driving out in the country to deliver the papers and regularly taking a roadie with him.
In some parts of the country, I don't think that would be all that out of the ordinary still.