What other rules apply to school bus drivers?
Because school vehicles are a "public place," drivers shall not smoke in the school vehicles at any time (including when there are no students present). Iowa Code - 142B.1(3). 142B.2(1).
Also, drivers may not permit firearms to be carried on the bus, and may not fill the tank with gasoline while the motor is running. 281 Iowa Administrative Code 43.38.