Minutes Matter: A Bus Transit Service Reliability Guidebook (2020) / Chapter Skim
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Pages 30-42
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30 4.1 Introduction This chapter provides information regarding Step 2 and Step 3 of a reliability improvement program: selecting reliability measures and selecting standards. It first describes the different types of measures for monitoring reliability, then presents an overview of the many measures that can be used to assess reliability identified through the review of the literature, the survey of transit agencies, and the detailed case studies.
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From page 31... ...
Reliability Measurement Tools 31 Three Aspects of Reliability Many different definitions of bus service reliability have emerged over the years, and there is a great deal of overlap and similarity between them. As time passes, however, researchers seem to be less interested in explicitly defining reliability and more focused on identifying the best measures and measurement techniques for tracking and reporting on bus service reliability.
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32 Minutes Matter: A Bus Transit Service Reliability Guidebook a range centered on a base value such as a mean, median, scheduled, or expected time. Such measures are easy to understand and to explain to the public but fail to capture the true variability of a service characteristic because they typically make an all-or-nothing assessment of an observation to determine whether it fits into an acceptable range.
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Reliability Measurement Tools 33 variability of travel times and of wait times. It is interesting to note, however, that none of the frequently cited measures in the literature address non-operation, even though the agency survey found that such measures are commonly used in the industry.
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34 Minutes Matter: A Bus Transit Service Reliability Guidebook "on-time performance" or "schedule adherence" was used, with varying targets and standards identified. Other less-used measures that agencies used as definitions included "missed trips," "travel time variability," and "vehicle reliability." Several agencies had no formal definition.
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Reliability Measurement Tools 35 At the system level, 87 percent of the 86 agencies responding indicated that they measured reliability performance. If an agency responded that it used a single performance measure, it was "on-time performance." On the other hand, one large agency indicated that it used almost all (15 out of 18)
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36 Minutes Matter: A Bus Transit Service Reliability Guidebook the route level. In the open-ended section, agencies indicated that some other measures they used were "hours of service interruption," "pullout adherence," "passengers/revenue hour," and "customer feedback." At the trip level, only 26 percent indicated that they measured reliability performance.
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Reliability Measurement Tools 37 are just different calculations from the same set of data. Table 4.2 presents a consolidated list of common measures grouped by the aspect of reliability addressed.
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38 Minutes Matter: A Bus Transit Service Reliability Guidebook trip, or stop level, different targets or thresholds may be used for a given measure to determine whether more detailed data or analysis is needed to determine the reasons for poor reliability. Most of the case study agencies set specific reliability targets for on-time performance and schedule adherence, ranging from a low of 60 percent [New York City Transit (NYCT)
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From page 39... ...
Reliability Measurement Tools 39 The first criterion requires further discussion, including consideration of the various definitions of reliability. The earliest definitions identified in the literature focused on variability and consistency of performance.
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40 Minutes Matter: A Bus Transit Service Reliability Guidebook group of measures rated as very good, good, fair, or poor depending on how well each group of measures addresses each criterion. A measure was given a rating of very good if it addresses the criterion in the most direct fashion.
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From page 41... ...
Reliability Measurement Tools 41 large sample of data from which to calculate reliability measures. The challenge for agencies often lies with developing the data management and reporting capabilities to analyze the huge amount of data collected.
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42 Minutes Matter: A Bus Transit Service Reliability Guidebook Among the 10 case study agencies, the medium- and large-sized agencies tended to have multiple departments involved. In some cases, such as LA Metro, it was a collaborative responsibility of several departments, including transportation, IT, planning, scheduling, and maintenance.
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