Various mechanisms may be used to preempt traffic signals so that emergency vehicles are provided with safe right-of-way as soon as practical. This type of preemption is typically used at intersections adjacent to fire stations and on commonly traveled routes. Communication with the traffic signals may be provided by direct wire, modulated light, or radio. The agency requesting the preemption is normally responsible for supplying the interconnect and any additional hardware required for the preemption. Agreements are not required.

Multiple preemptions are allowed at the same location. Priority must be given to each preempt. Railroad preemption always overrides emergency vehicle preemption.