What does the control tower require before allowing a vehicle to cross a runway?

The requirement for two-way radio communication before allowing a vehicle to cross a runway is essential for maintaining safety and coordination on the airfield. The control tower ensures that there is clear communication between the vehicle operator and the air traffic controllers, which helps prevent any misunderstandings that could lead to dangerous situations. By establishing two-way communication, the control tower can provide the vehicle operator with critical information regarding runway occupancy and aircraft movements, thereby ensuring that the vehicle only crosses when it is safe to do so. This protocol is a critical component of airfield operations, as it helps to manage the complex interactions between ground vehicles and aircraft.

The other options, while related to safety practices, do not fulfill the control tower's requirement for explicit permission to cross runways. For instance, while a visual assessment might be part of a driver's preparation, it does not replace the need for confirmed communication with the tower. Similarly, notification of aircraft schedules or surveying the surrounding airfield could be useful, but they do not provide the necessary clearance that two-way communication does.