I can't get a good answer for this as Google is thinking I'm talking just solely on the driver. I'm including passengers who don't. I've seen PSAs that tell you the dangers you pose for others as well when you don't wear a seatbelt. So if you don't wear a seatbelt and that results in someone being killed could you not wearing a seatbelt mean you get a manslaughter charge?
It still falls back onto the driver, as they chose to start driving without everyone buckled in.
What if the passenger unbuckles half way through?