Moin, I am proud owner of a Mercedes w123 200d bj 78 In the back the good piece has no straps, in the front already. That I can carry both rear and front people is clear to me and that children under 12 years / 150cm can only be carried with child seat. But since I do not take any children with me it doesn’t matter. The question is the passenger seat (with belt) must always be occupied if I am not travelling alone? Or can I theoretically take all 3 seats behind (no While the passenger seat is empty, I ask because it says: “mounted belts must be used.” There are 5 seats registered and I represent the opinion that I can decide who is sitting where (as long as they are not children) I am aware that it is better to drive with a seat belt and I ask myself for any kind of instruction, I am only concerned with the legal situation.