Takeoff Hold Lights (THL) These flush-mounted, in-pavement, unidirectional red lights are in a double row aligned with either side of the runway centerline lighting, and are directed toward the arrival end of the runway at the "line up and wait" point where aircraft are in position for takeoff or rolling, and extend for about 1,500 feet in front of the holding aircraft. Illuminated lights provide a signal to aircraft in position that it's unsafe to takeoff because the runway is occupied or about to be occupied by another aircraft or vehicle. For aircraft already on the takeoff roll, it may be impractical to stop for safety reasons. In this case proceed according to your best judgment while knowing that the runway is unsafe. Contact ATC at the earliest possible opportunity. Extinguished lights are not a clearance to begin a takeoff roll. All takeoff clearances will be issued by ATC. Ref. AIM Para. 2-1-6-c