What must be done before crossing any active runway?

Obtaining explicit clearance from Air Traffic Control is an essential prerequisite before crossing any active runway. This step ensures the safety of both personnel and aircraft by providing a direct confirmation that the runway is clear for your vehicle to proceed. Air Traffic Control has comprehensive awareness of all aircraft movements in the vicinity and can accurately assess whether it is safe for a vehicle to enter an active runway.

This process is critical because runways are busy areas where aircraft are landing and taking off, often at high speeds. By requiring explicit clearance, it minimizes the risk of potential collisions and maintains an organized flow of air traffic.

The other options may reflect safety measures, but they do not meet the regulatory requirement set by aviation authorities. Checking for other vehicles, looking for flashing lights, or proceeding only if no aircraft are visible do not replace the necessity of getting explicit clearance, which is the standardized procedure designed to prevent accidents in high-stakes environments like runways.