to prohibit a bus driver from stopping their bus in such a location as it would increase the possibility of an accident. It is a directive to the driver of the bus. It does not provide a defense to the driver of the vehicle that passed the bus.
Look at it this way;
even if you could not see the bus until you started to pass it, as long as those lights are on and sign out, you cannot complete the pass. While it might allow a judge to be sympathetic and reduce the penalty, it does not excuse the violation itself.

