Runway status lights

Runway Status Lights (RWSL) are a visual alerting system installed in some airport taxiways and runways for the purpose of collision-avoidance. When illuminated, red high-intensity LEDs indicate the presence of another vehicle either departing, occupying, or landing on an active runway. RWSL systems are fully-automated and intended to alert aircrews and ground vehicle operators of a potential runway incursion hazard. They operate as an additional layer of safety, independent of human-issued air traffic control clearances.^[1]

The system works by processing traffic position and movement data generated by transponders aboard aircraft and airside ground-vehicles such as aircraft rescue and firefighting (ARFF) units, aircraft tugs, and snow-clearing equipment. That data is concentrated by Airport Surface Detection Equipment (ASDE) or Airport Surface Surveillance Capability (ASSC) systems and fed to a path-predicting computer algorithm. If potential traffic conflicts are detected, the appropriate lights are automatically turned on or off according to the system's control logic.