CFD Emergency Vehicle Operations Course (EVOC) Practice Exam

Emergency signal preemption is the capability that lets an approaching emergency vehicle influence a traffic signal to favor its path. Opticom is a common preemption system fitted on many EMS vehicles. When activated, the vehicle’s device transmits a coded signal to a receiver at the intersection’s traffic controller. The controller then adjusts the light cycle so the vehicle sees a green (or an extended green) as it approaches, while cross-traffic is held red. This coordination can also link adjacent signals to create a smoother green wave, reducing delays and exposure to risk for the responders. Sirens, headlights, and beacon lights increase visibility or alert others, but they do not interact with or change the traffic light timing.