Application Areas

Signal Priority

Description

This field-to-vehicle application area covers the interface between a traffic signal controller and an emergency vehicle desiring signal preemption or a transit vehicle desiring signal priority. The granting of preemption or priority to the vehicle may be based upon passive detection of the vehicle type, or upon a request from an active device on the vehicle. Signal preemption typically implies that the controller switches the light to green in the direction of the preemption request, overriding the current timing. (However, there are other possible scenarios, such as setting all directions to flashing red.) Signal priority typically implies that the controller delays the phase transition so that a transit vehicle can get through the intersection. With signal priority the request for priority may or may not be granted, based on the overall traffic situation at the intersection.

National ITS Architecture Interface

This application area includes the interfaces between the Transit Vehicle Subsystem (TRVS) and the Emergency Vehicle Subsystem (EVS) and the traffic signal control equipment in the Roadway Subsystem (RS). The traffic signal controller in the RS receives a preemption request from the EVS or a priority request from the TRVS. The signal preemption interface for emergency vehicles is similar to the signal priority interface for transit vehicles; the difference lies in the level of priority given each type of vehicle. The vehicle requests signal preemption or prioritization using dedicated short-range communications to communicate with a controller for a particular intersection.

Applicable Standards

In general, the following standards are applicable to Signal Priority deployments. To determine which specific standards are applicable for a deployment you will need to determine which architecture flows will be needed for the Signal Priority piece of your deployment. Contact your local FHWA ITS Division Specialist or an ITS Standards Program Field Support Team contact

Standard	Development Status
APTA TCIP-S-001 4.0.0 APTA Standard for Transit Communications Interface Profiles;	Published
ASTM E2213-03 Standard Specification for Telecommunications and Information Exchange Between Roadside and Vehicle Systems - 5 GHz Band Dedicated Short Range Communications (DSRC) Medium Access Control (MAC) and Physical Layer (PHY) Specifications;	Published
IEEE 1609.2-2016 Standard for Wireless Access in Vehicular Environments - Security Services for Applications and Management Messages;	Published
IEEE 1609.3-2016 Standard for Wireless Access in Vehicular Environments (WAVE) - Networking Services;	Published
IEEE 1609.4-2016 Standard for Wireless Access in Vehicular Environments (WAVE) - Multi-Channel Operation;	Published
NTCIP 1201 Global Object Definitions;	Published
NTCIP 1211 Object Definitions for Signal Control and Prioritization (SCP);	Under Development

Deployment Resources

• DSRC (Dedicated Short Range Communications) Standards Advisory