A school bus on a four lane highway with a grassy meridian was in an exit lane going into a subdivision. It was parallel to, but not in the right lane. I was in the far left lane and it appeared to be a emergency response vehicle at first, upon moving closer I did not see any passengers in or outside the vehicle. The traffic in front of me kept traveling as if the bus was out of service. All of the documentation I've found indicate the bus being completely in the right lane and not off road. I cannot find any information pertaining to this situation, so it is not what my behavior should be in in this situation. Is there any other documentation on this?