During ground operations, when must vehicle operations not cross runway holding markings?

In the context of ground operations at an airport, vehicle operations must not cross runway holding markings until visual confirmation of departure is achieved. This guideline is essential for maintaining safety on the airfield to avoid potential collisions between vehicles and aircraft during takeoff or landing scenarios.

Visual confirmation indicates that the vehicle operator has verified through observation that the runway is clear and that it is safe to proceed. This helps ensure that no aircraft are on their final approach or departing while the vehicle is operating in the vicinity of the runway.

By adhering to this practice, vehicle operators contribute to overall air traffic safety and compliance with standard operating procedures that prioritize the order and efficiency of airport ground operations. The other options do not accurately state the situation regarding vehicle operations at runway holding markings. For instance, vehicle operations are not prohibited all times (as suggested by a choice related to continuous restrictions), as there are circumstances where crossing may be permissible with appropriate clearance and caution.