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Section 3: Preemption

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Preemption by Railroad Equipment

Traffic signals near railroad grade crossings can be connected to the railroad equipment to initiate a traffic signal preemption sequence. The railroad installs sensors on the tracks that send an electrical input to the traffic signal controller as the train passes over the sensors.

When To Use. Preemption of a traffic signal by the railroad signals is required if the traffic signal is at an intersection that is within 200 feet of a railroad grade crossing. Preemption should be considered wherever traffic may back up over the crossing due to traffic signals or other traffic congestion.

Traffic signal preemption requires an agreement with the railroad. For more information on railroad agreements and preemption, see the Rail-Highway Operations Manual.

Types of Railroad Preemption. Preemption of a traffic signal by railroad equipment may be either “simultaneous” or “advance.” These terms, which are used by the railroads, are explained in the Rail-Highway Operations Manual.

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Preemption by Emergency Vehicles

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.

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