At a drawbridge without a signal or attendant, what must a bus driver do?

When approaching a drawbridge that has no traffic signal or attendant to control crossing, a bus driver must stop at least 50 feet before the draw of the bridge. The driver may proceed only after confirming the draw is completely closed and it is safe to cross. A stop is not required if the bridge has a working traffic light showing green, or a guard or attendant controlling traffic, or if the bridge is a type that never opens for traffic. The rule prevents a bus full of passengers from driving onto a bridge that is open or opening.