3.0 Signal System Characteristics

In order to identify the key characteristics of signal systems that should be taken into account in the development of a SSAMS, the state-of-the-practice in signal system asset management was evaluated through a literature review, agency survey, and follow-up in-depth interviews. The detailed findings of the state-of-the-practice review were documented in an earlier report prepared for this project,¹ and are summarized below.

3.1 State-of-the-Practice Review

The state-of-the-practice review targeted mid-sized agencies (200 to 1,000 signals), which have a sufficient degree of complexity in their operations to merit a structured approach to asset management, but not such a large scale so as to create unique requirements or allow for major efforts that are not representative of the majority of agencies. In order to identify the “mid-sized” agencies, a copy of the latest (2000) ITS Deployment Tracking Survey² database was obtained from Oak Ridge National Laboratories. This database covered agencies in the 75 largest U.S. metropolitan areas. Figure 3.1 shows the distribution of agency size included in this database. Of 428 total agencies included in the ITS Tracking Survey database, 41 percent (176) have less than 100 signals; 21 percent (89) have between 100 and 200 signals, 32 percent (137) have between 200 and 1,000 signals, and the remaining six percent (26) have over 1,000 signals.

Figure 3.1  ITS Deployment Tracking Survey
Distribution of Agencies by Number of Signals

Twenty-six mid-sized agencies identified from the ITS Tracking Survey database agreed to participate in this state-of-the-practice review. These agencies were asked to provide information about the following three aspects of signal system operations and management:

1. Physical – The specific physical components that make up signal systems (e.g., signal heads, loop detectors, video cameras, controller boxes);
2. System – The capabilities and configuration of hardware, software and communications infrastructure that connects and controls the signal system to provide the traffic management function; and
3. Personnel – The staff resources available for operating and maintaining the signals and the institutional and management approaches used to provide these staff resources.

The data collection instrument was designed to gain insights into how agencies balance investments in these three areas as they maintain and improve their signal systems.

Results of the agency survey indicate that agencies are tracking and managing the physical, systems and personnel components of their signal systems at varying levels of sophistication, as appropriate to the scale and complexity of their systems. Tools and techniques are in place to optimize system performance for the road user; most agencies track performance of intersections or groups of intersections with respect to safety and delay, and use this information to identify improvement needs. As agencies upgrade signal management technologies, new real-time capabilities for performance monitoring and control will come on-line which will allow further performance gains to be realized.

With respect to the physical aspect of signal systems, most agencies have basic inventory tracking and maintenance management systems, but relatively few maintain data on failure rates and historical repair costs that would be needed to make a case for doing more preventive (versus reactive) maintenance. This type of data would also be needed to develop predictive capabilities in support of performance-based budgeting approaches. Given the agencies’ concerns with respect to budgetary and staff limitations and their desire to reduce repair costs, improved capabilities to both prioritize investments and to demonstrate what could be achieved with additional resources would be valuable.

Agencies are considering tradeoffs between technology and staff resources, and the application of asset management principles will increase the sophistication of this analysis.

Based on the data collected, the following conclusions can be drawn regarding the state-of-the practice in relation to the asset management principles stated in the previous section:

Policy-Driven and Performance-Based – Signal system goals and objectives focus on two major areas. One is performance of the system equipment in terms of reliability and function. The other is the level of service provided to the end-user in terms of throughput and safety. These areas are related in that unreliable equipment impacts the road user. Performance measurement for signal systems appears to be well understood and mature with respect to end user measures, particularly at the site-specific (as opposed to systemwide) level.

Analysis of Options and Tradeoffs – Based on agency ratings of priorities, it appears that practitioners do consider a variety of alternatives for signal system maintenance and improvement – spanning physical upkeep of existing components, upgrades to components, implementing new traffic management capabilities, additional coordination within and across jurisdictions, adding signals, adding staff, and building staff capabilities. However, resource limitations constrain the set of feasible options for improving system performance.

Decisions Based on Quality Information – Some agencies have implemented integrated management systems to link inventory data, maintenance management, and customer request management. Some are making use of signal management systems which support real-time monitoring and control. Simulation models are being used to improve signal optimization and maintenance management systems are providing improved information on equipment status. However, many agencies operate in a reactive mode and both staff and analytical tools for data reduction and analysis are scarce.

Monitoring to Provide Clear Accountability and Feedback – Maintenance management systems, traffic monitoring systems and real-time signal control and performance monitoring systems all offer the potential for a rich set of monitoring information that can be used to improve both day-to-day operations and longer-term strategic investment decisions for signal systems.

3.2 In-Depth Interviews

In-depth interviews were held with the Minnesota DOT Metro Division and the Wisconsin DOT Central Office Traffic Operations Group. These interviews supplemented the state-of-the-practice review, providing more detailed information on signal system management and operations that are necessary for defining the elements of a SSAMS. Key findings were as follows:

MnDOT Metro District

• System Size – The Metro District covers the Minneapolis-St. Paul metropolitan area and is responsible for 650 signalized intersections or about 50 percent of the signalized intersections under MnDOT jurisdiction in the State.
• Organizational Responsibilities – Signal maintenance and operations functions are provided by separate units. Signal maintenance functions include routine maintenance and repairs. These functions are carried out by electricians, electronic technicians, and locators (responsible for identification of underground utilities). The unit responsible for signal maintenance is also responsible for lighting maintenance. Signal operations functions include signal timing, and signal system upgrades and replacements. These functions are carried out by traffic engineers, signal technicians, and construction inspectors. In addition, several departments outside of traffic operations perform specialized functions – for example, the road maintenance department performs annual preventive maintenance inspections on electronic signal components.
• Monitoring – MnDOT tracks personnel hours, vehicle usage, and materials usage for maintenance/repair activities and capital projects. Complaints from the public (primarily related to equipment failures) are monitored. Maintenance records are kept and reviewed to identify failure patterns. MnDOT has also begun to systematically evaluate each intersection’s capacity and throughput.
• Operations, Maintenance, and Repair Strategies – Annual timing adjustments are made as needed based on intersection evaluation (and using guidelines for minimum cycle lengths); contractors are used to recommend and sometimes implement the new timing plans. Repairs are made in response to customer complaints/service requests. Repair guidelines are used to determine priorities for addressing these requests (e.g., equipment failure is highest priority). Analysis of failure patterns is used to identify replacement needs – by equipment type and location. Preventive maintenance is performed on all cabinets, filters, and bulbs twice annually. Contracts are let for cable and wire replacement, and “group relamping” activities (replacement of 3,000+ lamps at one time). Older signals are replaced (10 to 15 per year) – sometimes just the signal head (which has a shorter life) is replaced. The signal control system is maintained in-house.
• System Upgrades – New signals are added in response to traffic studies – the construction cost is shared with municipalities and with private developers. Most of the controllers have been modernized – many of these were accomplished as special projects. Upgrades to the signal control system are done by the vendor.
• Budgeting – There are separate budgets for maintenance and operations. The operations budget includes an allocation for preservation projects (rehabilitation and replacement of older equipment). Budget requests have been based primarily on historical trends, but a new maintenance management system is providing a better basis of information for forecasting of requirements from year to year. For major signal upgrades, intersections are prioritized based on safety considerations and volume.
• Key Tradeoffs – 1) Preventive versus responsive maintenance: preventive maintenance has been proven to be beneficial (e.g., the implementation of a preventive maintenance plan back in 1987 led to a decrease of 50 percent in signal malfunctions) but it has been difficult to fund it adequately and therefore much of the maintenance is reactive; and 2) life-cycle implications of new investment: Adding new signals to the network and introducing new technology to improve performance (e.g., video detection) has “downstream,” life-cycle impacts on maintenance and operations needs that are not anticipated or budgeted for. New ITS technology imposes up-front training requirements as well. Use of standardized equipment is preferred from an operations and maintenance perspective to ensure reliability and minimize training needs.

WisDOT

• System Size – WisDOT owns approximately 1,000 signals. Over 60 percent of these are in District 2, which includes the greater Milwaukee area. Others are maintained by the State through agreement.
• Organizational Responsibilities – WisDOT’s signal operations and maintenance function is split between the Central Office and the Districts. The WisDOT Central Office in Madison has two electricians that provide oversight to maintenance personnel in the eight districts. The Central Office also has a shop that builds cabinets. On the operations side, the Central Office has a signal group with six traffic engineers who do capacity analysis and signal design. The Central Office also executes statewide contracts for servicing controllers. District 2, which contains the majority of state-owned signals is the base for most of the electrical staff in the State. District 2 also has two people dedicated to safety and signal operations. In other districts there is generally a “lead worker” in signal operations and an engineer who is in charge of signal studies, design, and analysis. Depending on the size of the district, this engineer may have other duties as well.
• Monitoring – WisDOT tracks service requests, including response and repair times. Timesheet information is used to track labor hours for signal maintenance and repair activities.
• Operations, Maintenance, and Repair Strategies – WisDOT staff respond to service requests, though budgetary constraints and staff reductions make it difficult to address non-emergency requests. About five percent of signals are rehabilitated annually. Monitor checks are also conducted annually and refurbishing and rewiring is done where necessary.
• System Upgrades – Needs are identified through the annual six-year program update process. Corridor or area planning studies also help to identify future investment needs. Signal requirements are often generated through Traffic Impacts Analysis related to new development. WisDOT reviews these analyses and may identify the need for new signals or signal upgrades. This process allows for systemwide impacts to be identified and clearly documents the need for improvements. If the improvement required is not in an existing plan, the developer will pay the full cost. A cost sharing agreement will generally be negotiated between the developer and WisDOT if the improvement is already in the plan but not funded.
• Budgeting – Previous year’s budgets are reviewed prior to the annual capital budgeting process and are generally used as a guideline. A similar process is used for operations and maintenance budgeting. Improvements to inventory tracking are being made to establish annual budgeting requirements. Both Central office and District activities are being tracked to help estimate personnel requirements for the upcoming year.
• Key Tradeoffs – Budget cuts have forced WisDOT into a more reactive (rather than preventive) approach to system maintenance. Labor is the most constrained resource, and impacts on introduction of new components (such as LEDs) on personnel requirements are considered.

3.3 Overview of Signal System Characteristics

The information collected from the state-of-the-practice review and in-depth interviews has provided insights into the decision-making structure of signal system agencies. This section builds on these reviews, and identifies those characteristics of signal systems that need to be considered in order to determine the types of capabilities to be provided by a SSAMS.

Figure 3.2 provides an overview of the characteristics of a signal system that are relevant to the development of a SSAMS, and shows the logical interrelationships among these characteristics.

Figure 3.2 Signal System Characteristics

Each of these characteristics is discussed below:

• Physical Characteristics of the Signal System – The signal heads, structures, controllers, detectors, communications system, and central control hardware and software. Each of these physical components has a set of capabilities and a condition that affects its functionality and performance. While not illustrated in the figure, it is also important to recognize that because these different parts make up a system, the interconnections and dependencies among components must be considered. A hierarchical view of a signal system is needed to indicate subsystems and their member signals and controllers. Such a view would also allow for decomposition of signal heads, controllers, structures, detectors, and communications equipment into their component parts.
• Operational Characteristics of the Signal System – These encompass signal timing plans, coordination of different signals in the system, control strategies (e.g., fully versus semi-actuated operation, use of adaptive control), preemption and priority strategies in place, and other aspects of signal system design such as detector placement.
• Operating Environment of the Signal System – A description of the context within which the signal system operates and the demands that it must satisfy, which includes the characteristics of the road network, intersection geometry, presence of rail crossings, the current volume, composition and distribution of traffic (including percentage of trucks and buses), the variations in traffic patterns (and the degree to which these patterns are predictable based on season, time-of-day or day-of-week), pedestrian flows, and patterns of development affecting traffic growth. Other environmental factors such as temperature range and weather patterns can also be important characteristics that impact system requirements and performance.
• Performance Characteristics – Measures of how well the signal system is meeting objectives. Signal systems are typically evaluated based on traffic flow efficiency, throughput, reliability (failure rates or down-time), travel time and delay, and safety record (crashes). Performance characteristics are affected by the combination of the operating environment and the physical and operational characteristics of the signal system.
• Actions – Actions change the operational or physical characteristics of signal systems. There are many different ways used to categorize actions, but the following four basic types can be distinguished because they may be planned, budgeted and carried out using distinct sets of business processes.
  • Operation of existing signals (retiming, adding protected turn phases, modification to preemption or priority strategies).
  • Upgrades to signal systems (establishing a traffic management center, adding signals, connecting signals or changing the architecture for signal interconnections, adding new detectors to side streets, upgrading controllers, implementing adaptive signal control strategies, implementing new detector technologies).
  • Preservation of signal systems including inspection/testing and repair, rehabilitation or replacement of existing signals or signal system components based on observed condition or functionality, age, failure rates, or identified safety concerns.
  • Reactive or Remedial Repairs to correct damaged or malfunctioning equipment (e.g., signal knockdowns, lamp burnouts, detection failures, controller malfunctions, traffic progression problems, or safety risks).
• Resources are used to carry out work in order to impact performance. Five types of resources are distinguished here:
  • The existing internal agency staff resources, including traffic engineers, electricians, and technicians.
  • Expertise is called out as a separate resource, since it can be purchased in the form of training to enhance the capabilities of existing staff.
  • Vehicles used to perform signal system maintenance and repairs.
  • Equipment used to perform signal system maintenance and repairs (e.g., electronic test equipment).
  • Contracts are used to carry out capital projects and major maintenance activities – thus, they are also included as a resource. (From a day-to-day operations perspective, contracts in place are viewed as a resource to draw upon to perform actions (e.g., emergency repairs). From a longer-term planning perspective, contracts might not be classified as a resource, but rather as one method for obtaining labor, expertise, vehicles, and equipment resources.)
• Budgets – Resources are paid for out of budgets. There are typically separate budgets for capital, operations, and maintenance, though some agencies have a combined operations and maintenance (O&M) budget, some fund major maintenance projects from the capital budget and some agencies allow certain types of capital projects to be funded with O&M monies.
• Funding for signal system work comes from Federal, state, and local sources. It is common for signals projects to be funded with monies from private developers and from other jurisdictions. The funding source is important to consider, since it typically constrains what resources the funds may be used to pay for.

The next section of this report presents a model of a “generic” signal system based on a description of the above characteristics. Then, this model is used to define key elements of a SSAMS.

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