What is the phraseology used for vehicles or equipment near/on the runway?

The correct phraseology for vehicles or equipment near or on the runway is "Caution, runway active." This phrase serves as an important alert to pilots and air traffic controllers regarding potential hazards on the runway. It is crucial for maintaining safety during takeoff and landing operations, as it informs pilots that they should be vigilant due to the presence of other vehicles or equipment that may interfere with their movements.

The other options entail different meanings and situations. "Proceed as requested" indicates that a vehicle or aircraft is being given permission to move as they initially requested, but does not specifically alert pilots to a runway hazard. "Wait for clearance" suggests that a party should hold their position until they receive permission to move, which does not convey imminent dangers. "Maintain position until cleared" instructs an entity to stay where they are until specifically told to move, again lacking the direct warning about runway activity.

Thus, "Caution, runway active" is the most appropriate phraseology to ensure that everyone is alert to the potential risks posed by vehicles or equipment on or near the runway.