Traffic Signal Management Plans

Chapter 2. Operational Objectives and Performance

Meaningful performance measurement is a key tenet of achieving good basic service and is imperative to evaluating the achievement of objectives, the appropriateness of strategies, and enables the optimization of tactics. Performance measures link objectives, strategies, and tactics and are central to implementing performance-based planning and management processes. See FHWA's extensive resources for its Operations Performance Measurement Program at: https://ops.fhwa.dot.gov/perf_measurement

How you define and measure performance will significantly affect the types of strategies and tactics implemented and capital projects advanced to achieve them. Moreover, performance results inform agencies if the types of projects and strategies that have been implemented are, in fact, helping them achieve their goals and objectives.

The National Performance Review (cited in FHWA, 2015) provides the following definition of performance measurement:

A process of assessing progress toward achieving predetermined goals, including information on the efficiency with which resources are transformed into goods and services (outputs), the quality of those outputs (how well they are delivered to clients and the extent to which clients are satisfied) and outcomes (the results of a program activity compared to its intended purpose), and the effectiveness of government operations in terms of their specific contributions to program objectives. Output may measure the appropriateness of a strategy or the effectiveness of an activity, and is of direct interest to the agency. Outcome may measure the quality of an activity, and is of primary interest to the customer. Both may help to decide on resource needs, and the need for improvement in systems and technology via capital investments.

Examples of measures of effectiveness that describe outcomes are included in Table 1.

Table 1. Typical outcome performance measures.

Operational Objective	Strategy	Measure
Smooth flow	Provide pipeline	Percent arrivals on green
Throughput	Provide pipeline	Volume passing a critical points
Equitable access to adjacent land uses	Equitably distribute green time	Delay on all movements; Number of phase failures for each movement
Equitable access to adjacent land uses	Operate signals to optimize intersection efficiency	Percentage of "max outs" on each phase
Queue management	Prevent queue overflow	Queue lengths at locations where queue length is critical

Roles of Performance Measures

Performance measures serve five critical purposes within traffic signal management – they are used as follows:

• To clarify the definition of objectives – Metrics assist in conversion of broad goals into measurable objectives.
• To monitor or track performance over time – Metrics are used to track performance on a regular or on-going basis (e.g., yearly, monthly, continual).
• As a reference for target setting – Metrics are used as the basis for selecting a target that is intended to be achieved.
• As a basis for supporting policy and investment decisions by comparing alternative options – Metrics are used as a basis for comparing alternative investments or policies in order to make decisions.
• To assess the effectiveness of projects and strategies – Metrics are what enable measurement to assess whether projects and strategies have worked to further goals.

Two well-known challenges associated with defining performance measures are difficulties associated with data availability and difficulties in developing quantitative measures for goals such as economic vitality and livability. That is why performance measures identified for a TSMP should concentrate on objectives and strategies. See, for example, Gettman, et al. (2013) and Bullock, et al. (2014).

Factors to Consider in Selecting Measures

Selecting performance measures requires considering what specific metric will be used and how measurements will be taken. For more detailed discussion of performance measures, see the FHWA performance measurement website (FHWA, 2015), and discussion in Day, et al. (2014), Bullock, et al. (2014) and Gettman, et al. (2013). The operational performance objectives are selected within the context of location, traffic congestion, etc. In selecting a performance measure, several factors should be considered:

• Does it represent a key concern? The selected performance measure should play a role in decision-making within planning and management and relate clearly to goals established in a performance-based planning process. The selected measure will have important implications on strategies that are selected.
• Is it clear? Is the measure understandable to managers, policy makers, and the public? Avoid technical terms if not necessary.
• Are data available? Consider the feasibility and practicality to collect, store, and analyze data and report performance information for the selected measures. While data availability is important, it is important to also remember to not simply define the measure based on what data are readily available.
• Is the measure something the agency and its investments can influence? A good measure does not need to be something that an agency controls. However, it will be important to select measures that can be influenced through policy and investment decisions in order for the measure to be useful in supporting investment decisionmaking.
• Is the measure meaningful for the types of services or area? While consistency in metrics can be valuable, it is also important to make sure that a measure is meaningful to the area or system to which it is applied. Care must be taken to keep the focus on customers (such as on people rather than facilities and vehicles) to avoid unintended consequences.
• Improvement direction is clear. In some cases, agencies choose measures but do not state clearly whether they desire the measure to increase or decrease, which is particularly problematic when the measure could be interpreted differently depending on one’s perspective.

There often can be value in using multiple measures to address multiple dimensions of a problem. At the same time, it is advisable to start with a limited number of measures since it can be overwhelming to address hundreds of different measures. Experience suggests the importance of keeping the measures simple. It has been noted in many places: "Measure what is important; do not measure everything." Avoid measures that may provide useful information but may not be key considerations in relation to identified goals, making an agency "data rich but information poor."

Appendix. A contains four case studies, each of which shows very effective use of one measure of performance to assess how well a traffic signal management objective (or strategy) is being met. The four cases described are summarized in Table 2.

Table 2. Summary of Performance measure case studies.

Objective or Strategy	Performance Measure	Data Collection Method	Agency
Provide smooth flow on arterial	Percentage arrivals on green in corridor	Automatic high resolution data and Purdue Coordination Diagram	Utah Department of Transportation
Maintain stable travel times over time	End-to-end travel time on specified corridors	Annual floating car surveys Automatic using Bluetooth readers	City of Mesa
Provide travel time commensurate with level of demand	Corridor segment travel time	Automatic using Bluetooth readers	City of Walnut Creek
Maintain signals in good state of repair and operating in a manner for which they were designed (Strategy: proactively maintain detection reliability)	Signal timing complaints	Automated high performance controller data analysis and reporting	Utah Department of Transportation

There are several different layers of performance measures, each of which are essential to effective management of a traffic signal system. At the decision-maker level, measurement of the effect of traffic signal operation on the various road users will quantify how well the objectives are being met (measuring the outcomes). These measures will all be directly observable by the users, such as trip times, fuel consumption, air quality and quality of service measures.

At the strategic and tactical levels, it is the signal manager's responsibility to measure the implementation of activities against established standards, to ensure they are being done effectively and efficiently. These measures generally relate directly to the performance of staff (outputs). Examples of measurements of the performance of a strategy of providing proactive maintenance are shown in Table 3. Examples of measures that quantify the outcome of the implementation of the same strategy are shown in Table 4.

Table 3. Output performance measures.

Objective	Strategy	Tactic	Measure
Maintain the traffic signal system so it always operates as intended	Undertake proactive maintenance	Test pedestrian detectors	Number of detectors tested Number of failed detectors reported
		Clean and realign signal heads and lenses	Number of heads cleaned Number of heads requiring realignment

Table 4. Outcome performance measures.

Objective	Strategy	Measure
Maintain the traffic signal system so it always operates as intended	Undertake proactive maintenance	Number of emergency maintenance callouts per unit (e.g., per signal, per month) Number of reported malfunctions per unit
Undertake maintenance in a cost-effective manner	Undertake proactive maintenance	Ratio of emergency maintenance to total maintenance expenditure