The Relationship Between Transit Asset Condition and Service Quality (2018) / Chapter Skim
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Pages 26-34
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26 Guidance for Calculating Effects of Changes in Asset Condition on Transit Service Quality Overview This chapter provides guidance on calculating the effects of changes in asset condition on transit service quality. The measure, Effective Journey Time (EJT)
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Guidance for Calculating Effects of Changes in Asset Condition on Transit Service Quality 27 Key Concepts and Assumptions EJT Example Figure 3-1 showed an example of a baseline calculation of EJT, and an example of the improvement in EJT that might result following improvements in asset condition from an SGR investment. The figure shows three basic components of EJT: buffer time, wait time, and IVT.
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28 The Relationship Between Transit Asset Condition and Service Quality • The analysis approach is intended for use in predicting EJT for frequently operated fixedroute service for buses, bus rapid transit (BRT) , and rail (light rail, heavy rail, and/or commuter rail)
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Guidance for Calculating Effects of Changes in Asset Condition on Transit Service Quality 29 includes station facilities, or in the case of rail systems, one must decide whether to include station facilities, as well. Further, for rail systems one may or may not wish to consider potential guideway failures.
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30 The Relationship Between Transit Asset Condition and Service Quality data requirements for the simplified and comprehensive approaches. Data items required for the specified calculation approach are indicated with a check mark.
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Guidance for Calculating Effects of Changes in Asset Condition on Transit Service Quality 31 Data Item How Addressed in Each Approach Simplified Comprehensive Vehicle failures Initial MDBF is directly entered, or approximated based on vehicle type and fleet age. Change in MDBF is approximated based on TCRP Report 157 models.
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32 The Relationship Between Transit Asset Condition and Service Quality The analyst should review the data requirements and assumptions for each approach, and in this step select which to use for the analysis. As a general rule of thumb, the Comprehensive Approach is required for complex cases, and recommended where sufficient data are available to support it.
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Guidance for Calculating Effects of Changes in Asset Condition on Transit Service Quality 33 Step 5 -- Summarize Results The final step is to compile and summarize the analysis results. Depending on the scope of the analysis and calculation approach, one may obtain one or all of the following metrics for the base and future cases: • EJT per passenger • EJT per passenger mile • Total EJT The analyst may wish to supplement these with • Percentage change in EJT between the base and future scenarios • Unadjusted journey times per passenger • Total journey cost (obtained by multiplying the per passenger results by number of passengers)
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34 The Relationship Between Transit Asset Condition and Service Quality Although EJT is valuable as a single measure that summarizes transit service quality, no one measure can properly reflect all of the dimensions of service quality described in Chapter 3. It may be helpful to supplement the presentation of EJT results with a qualitative description of the changes in service quality expected from a predicted improvement in or worsening of asset condition.
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