Looking for a title!

I remember watching a clip a few years ago. I'm not sure if it's a movie or a show, but I think it's Japanese. A bunch of students were riding a bus and a girl drops something on the floor, so she goes to pick it up. When she does, something from a truck in front of them falls off and flies towards the bus. As a result, the top half of the bus gets cut off along with all the passengers' heads. The girl who dropped something survives because she was crouching when it happens.