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69 6 CONCLUSION The Guide to Incorporating Reliability Performance Measures into the Transporta- tion Planning and Programming Processes provides guidance on how agencies can plan and make investment decisions that address fluctuations in travel time that result from variations in demand, incidents, weather, special events, and other factors. These fluctuations in travel time define the reliability of the systemâthe ability of its users to predict the amount of time it takes to make a trip or make a delivery. Addressing reliability requires first understanding the locations and sources of travel time variability. This typically requires a significant amount of travel time data and, ideally, information about related conditions (e.g., incidents, weather). SHRP 2 L02 provides guidance on developing a travel time reliability monitoring system that can help agencies identify the data needed to measure system reliability, as well as approaches to organizing and managing those data to help understand system reli- ability. Developing an understanding of reliability provides a foundation to using reliability within the planning and programming process. The guide addresses three key aspects of the planning process. Defining policy statements. Based on travel time and other data and stakeholder input, agencies can identify how reliability should be addressed among other agency goals and objectives. Estimating needs and deficiencies. Having established reliability as a priority, understanding needs requires setting threshold levels for acceptable and unacceptable system reliability (i.e., defining good, fair, and poor reliability) and estimating system needs. Needs can be defined by examining individual potential investments or catego- ries of investments. Both performance-based and economic analysis approaches can be used, potentially in combination. Defining needs and deficiencies helps agencies understand the scope of their reliability challenges.
70 GUIDE TO INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES Supporting investment decisions. Building on the understanding of system needs, agencies must determine how they are going to fund investments in operations and management programs relative to other program areas. Then agencies can use this information to help prioritize projects, either within or across program areas. Support- ing decision making requires a performance-based approach and analytic tools that agencies can use to both estimate and forecast reliability performance and the impact of investment strategies on future performance. Traditional planning tools, such as four-step travel demand models, are not well suited to address reliability because they produce static estimates of travel times. The SHRP 2 Reliability program has devel- oped a set of both sketch-planning and more sophisticated methods to help agencies either use the tools they have or develop new tools to forecast future reliability. Significant detail on the tools and methods can be found in the accompanying technical reference, case study technical memorandum, and final report. Although the technical reference provides up-to-date information on these tools and methods, given the evolving state of the practice, emerging methods will continue to change over time, requiring revisiting these issues over the next 5 to 10 years. As agencies update their tools, they will be better positioned to tackle the reliability of the transportation system.
