Who must grant clearance before a vehicle can enter a controlled taxiway?

Clearance before a vehicle can enter a controlled taxiway must be granted by Air Traffic Control (ATC). This is because ATC is responsible for managing air traffic on the airport surface and ensuring the safety of all operations involving both aircraft and vehicles. They coordinate movements and provide instructions to maintain safe distances between aircraft and vehicles, preventing potential accidents.

ATC maintains an up-to-date awareness of all movements on the airfield and can communicate directly with vehicles and aircraft to manage their movements effectively. In critical environments like a controlled taxiway, where aircraft are moving, the authority provided to ATC ensures that only vehicles cleared by them can enter, thus maintaining operational safety and efficiency.