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This section presents a description of a fictitious signal system, operated by the traffic operations division of the City of “Anywhere USA,” based on the key characteristics identified in Section 3.0. A medium-sized system is described, of sufficient scale to benefit from application of a systematic asset management approach, but not so large as to require highly sophisticated or unique approaches. This concrete example will be used to help define the capabilities, features, and procedures needed to do signal systems asset management, and to develop a high-level architecture for a SSAMS.
The City of Anywhere’s traffic engineering division is responsible for a 640-mile arterial network with 405 signalized intersections. Anywhere is a medium-sized suburban community of 200,000 population, located within a metropolitan area of 1.2 million. Most intersections are currently operating at level of service C or better. However, traffic on the arterial system in the western portion of the City has been growing at the rate of three to four percent per year, which has created the need to add new signals to the network and adjust timing plans at many intersections each year.
One hundred fifteen of the 405 signalized intersections are under closed loop control. The system has 20 master controllers, and 165 local controllers – five signals are flashing and have no controller. All of the controllers are based on NEMA TS-1 and are not NTCIP-compliant. The communication network consists of dial-up telephone lines from the traffic management center to various on-street master locations and either dedicated copper or fiber optic lines from master to local controllers.
Twenty intersections have loop detectors; 10 have video detectors. 170 signals allow preemption by emergency vehicles.
A traffic management center is in place, housing two personal computers running the central control software, video monitors, and communications devices.
Objectives for the Anywhere signal system are to maintain or improve current traffic speeds in arterial corridors, to improve reliability of signals, and to reduce crashes at intersections where the crash rate exceeds the regional average. Performance measures that are tracked include: number of crashes at signalized intersections, mean time between failure (MTBF) for signal components, and mean time to repair (MTTR). In addition, intersection vehicle hours of delay are evaluated as part of intersection and corridor traffic studies.
The division has a manager, two traffic engineers, two maintenance supervisors, five electricians, 10 signal maintenance technicians, two utility locators, and two construction inspectors.
Outside contractors are used for major preventive maintenance activities (e.g., relamping), and to provide support for signal timing and intersection traffic control design.
The two traffic engineers have their professional engineer’s licenses. All other staff have associates degrees and have completed training programs for their areas of responsibility. Special training is provided to staff in conjunction with any upgrades to equipment or software.
The division has 10 hydraulic lift trucks.
The equipment inventory consists of 20 two-way radios, 20 cellular telephones, electronic test equipment, a stock of spare parts, power tools, hand tools, and other standard maintenance equipment such as ladders, shovels, and brooms.
The annual capital budget is $3,000,000, which is used to fund system upgrades and larger preventive maintenance projects. The annual operations and maintenance budget is $2.1 million, which funds salaries, equipment, and materials.
Signal timing is reviewed for roughly half of the intersections each year, and adjustments are made as needed in response to changes in traffic patterns.
Traffic control software is used to monitor signal operations, update system parameters, and dispatch repair crews to address operating concerns.
Roughly three to four new signals are installed each year, after traffic analysis has demonstrated that they are warranted.
A corridor project is underway to re-design traffic control for 10 intersections, and includes upgrades to controllers, installation of new detectors, and connecting previously isolated intersections.
A five-year program to replace older plastic signal heads with aluminum die cast heads is underway.
System software is due to be upgraded within the next two years.
An advanced traffic management study is planned, to develop a strategy for upgrading software and controllers and implementing adaptive control at selected intersections.
Signal equipment, controllers, and detectors are inspected twice per year, and repairs are made as needed. All electronic components are tested for proper functioning. Signal indication lenses are cleaned/relamped.
Sixty signal poles are painted each year; four to five are replaced.
In the past year, the division responded to:
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