Table 1: summary of transit signal priority deployment results

3.0 System Requirements

3.1 General Requirements

A. A major requirement of the system is to provide emergency and transit vehicles a specified form of preferential signal treatment in a safe and efficient manner at selected, signalized intersections along U.S. Route 1 in Fairfax County, Virginia. The system must be fully functional, reliable, easily maintainable, easily expandable, and easily upgradeable to new technologies and requirements. The system shall also be compatible with existing Fairfax County Fire and Rescue opticom equipment. To this end, the system should use to the largest extent possible commercially available off-the-shelf components with well-established records of reliability and performance. An underlying objective of this system is to improve emergency vehicle and transit travel time and to increase safety along U.S. Route 1. Other system requirements are stated below.

B. The installation of the emergency vehicle preemption and transit priority system will be at seven intersections along U.S. Route 1 as shown in the Exhibit B. An aim of this installation is to examine the functionality of the system when emergency vehicles and transit buses pass through the intersections. Vendor shall supply four (4) in vehicle devices for emergency vehicles and six (6) in vehicle devices for transit vehicles. Vendor shall also supply and install fifteen (15) detectors/readers in the specified intersections. The installation of in vehicle devices shall be done in coordination with the respective agencies.

C. The Vendor shall maintain the system for ninety (90) days following the acceptance of the equipment by VDOT.

D. The system shall be able to detect a vehicle within 500 to 1000 ft from the intersection.

E. An emergency vehicle shall be provided an “unconditional” green interval (i.e. preemption) in a safe and efficient manner as soon as all other necessary movements are provided a red interval.

F. A transit vehicle shall be provided a “conditional” green interval (i.e. priority) only if certain conditions prevail (e.g. no emergency vehicle request has been made and the existing interval in the direction of the transit vehicle is green and thus only a limited, green extension will be provided; if the signal interval in the direction of the transit vehicle is red when the transit priority request is made, the request is ignored).

G. Each preemption and priority request shall be acknowledged with a confirmation device. The priority device shall provide confirmation outports.

H. The system shall log preemption and priority requests, including but not limited to date, time, direction and vehicle ID. Preemption and priority requests shall be given only to vehicles with valid vehicle ID’s.

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