In the interests of accuracy, Eagle Wing, to my knowledge black people in the USA never used separate buses from the white people. They were required to sit at the back of the bus- and if the bus filled up with more whites, the blacks were required to move to the farther back seats.

Which is what Rosa Parks refused to do. As a matter of law, she was supposed to move farther back in order to let a white have her seat. When the bus driver told her to move, she refused and was arrested. And that's where the US civil rights movement began.