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From page 64... ... 63 5 CONDUCTING A RELIABILITY ANALYSIS Color versions of the figures in this chapter are available online: http://www.trb.org/Main/Blurbs/168856.aspx This chapter provides a systematic approach for conducting a reliability analysis using the reliability tools and methods described in Chapter 3. Each application of these various tools and methods may vary because of differences in the purpose of the analysis, input data availability, performance characteristics of the corridor or region being analyzed, and the desired outcomes of the analysis. Read the entire page →
From page 65... ... 64 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE 5.1 APPLYING SKETCH-PLANNING METHODS A reliability analysis using the sketch-planning method would be expected to follow these steps. Step 1: Confirm the Analysis Scope of Work The temporal (e.g., peak hour, peak period) Read the entire page →
From page 66... ... 65 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE Step 3: Determine Appropriate Sources of Data and Compile Data related to each of the segments defined in the previous step should then be assembled from available sources identified during the tool selection process outlined in Chapter 4. For the sketch- planning method, analysts should assemble data representing the overall mean travel time index (TTImean) Read the entire page →
From page 67... ... 66 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE Figure 5.2. Sketch-planning decision tree. Read the entire page →
From page 69... ... 68 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE TTIm = 1.0274 * RecurringMeanTTI1.2204 (5.5) Read the entire page →
From page 70... ... 69 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE Changes in incident frequency are most commonly affected by strategies that decrease crash rates. However, crashes are only about 20% of total incidents. Read the entire page →
From page 71... ... 70 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE spreadsheets require the users to input capacity, volume, and length of segment and use IDAS lookup tables in conjunction with the SHRP 2 L03 data-poor equations to produce several measures of reliability, including the mean TTI, 50th percentile TTI, 80th percentile TTI, and 95th percentile TTI/PTI. It also produces a measure of overall delay that includes nonrecurring delay using the relationship of the economic value of average delay to nonrecurring delay. Read the entire page →
From page 72... ... 71 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE = + = +   =t x1 0.2 FFS 1 0.2 3125 4145 65 0.0156 hours/mile 10 10 Average travel time for Segment 2 (a congested freeway segment with V/C greater than 1) was calculated as follows (from Equation 5.4) Read the entire page →
From page 73... ... 72 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE To assess improved conditions, Knoxville TPO first identified the assumed impacts of the improvement strategies in terms of decreased incident frequency, incident duration, and delay. These are summarized in Table 5.4. Read the entire page →
From page 74... ... 73 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE TABLE 5.5. KNOXVILLE TPO SKETCH MODEL IMPROVED CONDITION EXCERPT Segment Increased V/C for Speed Improved Speed and Delay Estimates Reliability Measures Speed TR Incident Delay (Da) Read the entire page →
From page 75... ... 74 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE Washington State DOT examined the mean TTI results to identify reliability deficiencies along the corridor. Based on knowledge gained of reliability performance measures in the state, the SHRP 2 L05 team applied professional judgment to set an initial mean TTI threshold of 1.5 to represent "unreliable" conditions. Read the entire page →
From page 76... ... 75 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE Washington State DOT used Equation 5.9 from this technical reference to estimate the impact of reduced incident duration and reduced crashes. Decreases in volume and increases in capacity and speed were used to estimate benefits directly. Read the entire page →
From page 77... ... 76 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE • They are not usually sensitive to the effects that upstream bottlenecks and blockages can have on downstream service rates. • They implicitly assume that all vehicle trips identified within the origin– destination matrix will be completed by the end of the time period being analyzed, regardless of whether there is actually sufficient capacity to accommodate these vehicle trips within the specified time window. Read the entire page →
From page 78... ... 77 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE need to occur in an interim step to ensure the data are input in the specified format (e.g., capacity values must represent per lane capacities over the selected analysis period) Read the entire page →
From page 79... ... 78 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE advances in overcoming the challenges related to identifying and quantifying nonrecurring congestion and the impacts of strategies in mitigating the negative impacts. These initiatives and their findings, discussed in Section 5.5, are useful when adjusting the demand model to represent capacity reductions associated with weather and construction events. Read the entire page →
From page 80... ... 79 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE This option may require more upfront effort to develop, configure, and test the customized routines, but this option may provide more seamless analysis later in the study, since it avoids the tedious exchange of data between the travel demand model and the IDAS application. The extra development effort may be particularly justified in analyses that will require a large number of alternatives to be analyzed or in situations where the analysis will need to be repeated in future assessments. Read the entire page →
From page 81... ... 80 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE the requirements of the reliability analysis. If a simulation model is not available and needs to be created, the analysis requires significantly more effort, expertise, and time. Read the entire page →
From page 82... ... 81 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE and travel demand model should cover the temporal and geographic scope defined in Step 1. For example, if a reliability analysis is desired for the p.m. Read the entire page →
From page 83... ... 82 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE Figure 5.4. Simulation method flow chart. Read the entire page →
From page 84... ... 83 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE or data collection plan should be organized in such a way that the number of days (or hours of delay) related to each scenario can be determined. Read the entire page →
From page 85... ... 84 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE essentially the variability in travel times extracted from the various scenarios for each strategy/ alternative, weighted by their probability of occurrence, is the reliability for that strategy/ alternative. Appendix D provides additional information on completing a multiscenario post-processing method based on probability of occurrence. Read the entire page →
From page 86... ... 85 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE • Computational Methods: how probability density functions can be derived from the variety of data sources. This includes the process of generating travel time probability density functions that can be used to derive a variety of reports to users. Read the entire page →
From page 87... ... 86 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE • Causal Factor Analysis: how the TTRMS can be used to examine the influence on reliability of various causal factors, both internal and external. The basis of the diagnostics presented in this section is the development of separate travel time distributions for a facility based on the presence of an "influencing factor." Thus, separate travel time distributions are developed when incidents, inclement weather conditions, work zones, and special events are present. Read the entire page →
From page 88... ... 87 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE Florida DOT uses both real-time roadside detection and probe data sources for their data collection efforts (see the Florida DOT case study for additional information) Read the entire page →
From page 89... ... 88 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE for all travel time reliability indices, once the travel time data are made available then the calculations themselves are simple for the computer to process. The most common reliability factors are the buffer time index, the travel time index, and the planning time index. Read the entire page →
From page 90... ... 89 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE 5.5 DEVELOPING MULTISCENARIO ALTERNATIVES Multiscenario methods are most often associated with simulation model methods but can also be used in conjunction with model post-processing methods and even sketch-planning methods. The basis of a multiscenario method is the development of scenarios that together combine to represent the variable events that occur to create nonrecurring congestion. Read the entire page →
From page 91... ... 90 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE To develop scenarios representing these nonrecurring conditions, the analyst will need to make modifications to the baseline parameters in the model used to reflect the capacity loss of these nonrecurring conditions. As part of the development of the Guide for Highway Capacity and Operations Analysis of Active Transportation and Demand Management Strategies, a number of baseline capacity constraints have been mapped to various nonrecurring conditions based on data in the 2010 Highway Capacity Manual (HCM) Read the entire page →
From page 92... ... 91 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE nonrecurring conditions need to be carefully considered, however, as each additional scenario will require additional time and resources to create and run. In addition, it is important for the analyst to remember that in order to conduct a benefit–cost analysis of TSM&O strategies, each of the scenarios will need to be run twice, once as baseline without the strategy and once as an alternative scenario with the strategy deployed. Read the entire page →
From page 93... ... 92 INCORPORATING RELIABILITY PERFORMANCE MEASURES INTO THE TRANSPORTATION PLANNING AND PROGRAMMING PROCESSES: TECHNICAL REFERENCE 5.6 REFERENCES 1. Akçelik, R Read the entire page →

From page 64...

... 63 5 CONDUCTING A RELIABILITY ANALYSIS Color versions of the figures in this chapter are available online: http://www.trb.org/Main/Blurbs/168856.aspx This chapter provides a systematic approach for conducting a reliability analysis using the reliability tools and methods described in Chapter 3. Each application of these various tools and methods may vary because of differences in the purpose of the analysis, input data availability, performance characteristics of the corridor or region being analyzed, and the desired outcomes of the analysis.