Bus's that don't stop

Last week Ms. Bowles came into class and told us how she had walked to class that day. She said she tried to catch the bus along the way because it was coming, but the bus drove right past her. Little did I actually know how annoying it is to have a bus just drive by you until a few days ago. My teamate China and I were outside JPJ waiting for a bus for a considerable amount of time, and when the bus finally came it drove right by us. The bus was no where close to being full either. Why does this happen? Are there certain procedurals one has to do to stop a bus? Does one have to make eye contact with the bus driver? Does one need to walk towards the bus as its passing to imply they want to get on? Are there unspoken bus waiting codes? Or is it that the bus driver just didn't see people waiting? hmmm...