Wow.. that's pretty terrible. Not all buses have seatbelts though, and even if there was, a lot of people won't use it, as no one is expecting something to happen like that... But anything could happen in China....
Was this the one that the truck driver missed the exit on a freeway, then decides to stop, then reverse to attempt to make an exit on the exit he missed? If that is so, that is fucked up itself. But yes, always wear your seatbelts. They're there for a reason. Pains me to watch Korean show sometimes and I don't see the celebrities wearing seatbelt.
