Under what circumstances may a bus driver operate the vehicle with an emergency exit door or window open?

AAMVA CDL Manual Section 4.1.3, p.4-1; 49 CFR 383.117(a)(2)

An open emergency exit while underway is a fall-out hazard for riders and can also let an unsecured door swing and strike something outside the bus. This is also directly tested under the federal passenger endorsement knowledge requirement covering proper use of emergency exits, which makes it one of the highest-yield facts to know cold.