At least in Germany it is. As reported by Reuters (a few years ago):
A Cologne court fined a man who admitted he was having sex with a hitchhiker sitting astride him when he drove his car into a road sign. But only because he fled the scene of the accident with his naked accomplice.
Said a court spokesman:
“It’s hard to believe but in fact no law was broken with the intercourse on the motorway. It’s a situation lawmakers never thought about.”
Is this a story these folks will be telling their grandkids? Unlikely.
[The driver] did not know the name of the woman who left her clothes behind in the car.