Unless permission is granted by Air Traffic Control Tower, under no circumstances shall a vehicle...

The correct answer highlights a critical safety protocol at airports. Vehicles crossing an active runway without explicit permission from the Air Traffic Control Tower pose significant risks to both aircraft and ground personnel. Active runways are designed for aircraft takeoff and landing, and unauthorized vehicle presence can lead to dangerous situations, including potential collisions.

Air Traffic Control is responsible for maintaining the safety and efficiency of airport operations, and they will only permit such crossings when it is safe to do so. This procedure minimizes the risk of accidents and ensures that all vehicles remain coordinated with aircraft movements.

While other options involve unsafe actions, they do not present the same level of direct risk as crossing an active runway without permission. Stopping on a runway or driving over a taxiway can also be problematic, but the act of crossing an active runway is particularly hazardous due to the immediate presence of aircraft in motion. Therefore, compliance with this restriction is paramount for maintaining safety at the airport.