What must a bus driver do at a drawbridge that does not have a signal or attendant?

Federal rules require a bus to stop at least 50 feet before a drawbridge that does not have an attendant or signal, look both directions, verify the bridge is fully closed and locked into position, and only then proceed at a controlled speed. Drawbridges that may rise can leave a gap or unstable surface, and there have been historical incidents of buses driving onto opening or partly-open bridges. Bridges with active signals (red/green lights) or attendants on duty are treated like railroad crossings — proceed when the signal indicates safe passage. The stop-and-verify rule applies regardless of whether the bridge has been raised recently.