Special Signal Functions

Traffic Signal Preemption

The transfer of normal traffic signal operation to a special operation is called preemption. There are three common types if preemption: Railroad Train, Emergency Vehicle, or Bus/Transit Vehicles.

Railroad Preemption

Railroad preemptions happen when a train passes over detectors located on the tracks ahead of the railroad crossing. The purpose of the preemption is to clear tracks of traffic stopped on them by traffic signals.

Emergency Vehicle Preemption

In the City of Woodland, fire engines are the only emergency vehicle to use preemption. The purpose is to shorten response time by turning on a green light for the fire engine as soon as possible or holding an existing green light. In order for a fire engine to obtain a green light, existing green lights, including the pedestrian interval, are shortened. The fire truck uses a strobe light to trigger a detector that is mounted on the signal.

Bus / Transit Vehicle Preemption

The bus / transit vehicle preemption system is not used in the City of Woodland.