The core idea is good. A law that isn't enforced is just a recommendation. There will be plenty of people who will just ignore it. Not unique to car drives, there are pretty much the same amount of people ignoring traffic laws with every transportation method, just when the size of the transportation method increases, so does the damage it can cause.
It would be kinda unfeasible for the bus driver to start writing down each cars license plate that passes by it when the bus has stopped. So similarly to speeding cameras which do lower the speed of cars within it's area of influence. A bus will carry around an area of influence inside which drivers are more inclined to follow the law.
Of course reality is that the system will be abused and badly implemented.