In numerous U.S. traffic signals, a small light positioned between or beside the regular lights serves as a priority or preemption signal.
These lights, often seen blinking during emergency vehicle passages, are part of a system enabling vehicle operators to override standard traffic light operations.
Maricopa County, Arizona, implemented Emergency Vehicle Preemption (EVP) systems in the early 1980s to enhance response times.
Equipped with emitters, emergency vehicles communicate with signal-receiving devices, activating a preemptive cycle that grants them immediate right of way through traffic lights.
Preemptive indicators, sometimes with confirmation lights, help emergency vehicles reach scenes faster.
The lights, whether steady or flashing, convey specific meanings, such as granting a green light in the activated direction or a different one.
Various systems employ line of sight, GPS, or radio signals to secure the right of way.
Some regions, like Pennsylvania, interpret steady and flashing lights differently, influencing the granted green light direction.
In a notable case, South Georgia Medical Center equipped its ambulances with GPS-ready EVP devices, reducing average response times by 11 seconds per traffic light, as announced in June 2023.
