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From page 44... ... 44 S E C T I O N 5 5.1 Introduction This section describes tools and approaches for applying the framework described in Section 4 to evaluating rehabilitation and replacement for specific types of transit assets. Section 5.2 summarizes the recommended analytical approach to prioritize rehabilitation and replacement alternatives and evaluating rehabilitation and replacement of existing transit assets, with guidance on models for specific asset types. Read the entire page →
From page 45... ... 45 5.2.1 Prioritization Model The objective of the prioritization model is to recommend a set of rehabilitation and replacement alternatives to perform to maximize utility. Section 4 discusses the concept of a utility function and addresses the objectives one might include in a utility function for evaluating transit asset rehabilitation and replacement. Read the entire page →
From page 46... ... 46 if performing a typical benefit-cost analysis in which one compares the alternative of performing a project to not performing a project. Because the benefits that are calculated are 1-year benefits of performing needed work relative to deferring action, any alternative with positive benefit (and thus, any non-zero value of PI) Read the entire page →
From page 47... ... 47 5.2.4 Age-Based Asset Model The age-based model is intended for use in prioritizing replacement actions for assets other than vehicles that replacement can best be predicted based on asset age. The model predicts the probability of asset failure using a Weibull distribution. Read the entire page →
From page 48... ... 48 • Age-Based Modeling Tool: this tool uses information on how an asset (other than a vehicle) deteriorates over time and the target replacement cycle for the asset to predict the annualized transit agency and user costs of the asset, as well as the priority of asset replacement as a function of age. Read the entire page →
From page 49... ... 49 Figure 5-2. Prioritization model inputs. Read the entire page →
From page 50... ... 50 and the number of vehicles in typical consist or train for rail vehicles; and • Discount Rate – this parameter quantifies the time value of money and should be set according to transit agency policy or left at its default value if the transit agency has not specified a specific value to use for analysis. In addition to these parameters, one can specify an additional set of detailed parameters. Read the entire page →
From page 51... ... 51 Figure 5-4. Vehicle model inputs. Read the entire page →
From page 52... ... 52 for the asset. For instance, facilities or systems would typically be characterized according to cost per asset, while guideway-related costs may be specified in cost per lineal foot or yard; and • Assumed Replacement Age – age at which the asset is assumed to be replaced, used for predicting future costs of an asset. Read the entire page →
From page 53... ... 53 • Discount Rate – this parameter quantifies the time value of money and should be set according to agency policy or left at its default value if the transit agency has not specified a specific value to use for analysis; • Shape Parameter – model parameter set by asset type that describes the degree to which the probability of failure changes as a function of age. Values of 1 or greater indicate the asset is more likely to fail as it ages. Read the entire page →
From page 54... ... 54 replaced, would fail by a given age) and the conditional probability of asset failure (probability the asset will fail in the next year, if it has survived to a given age) Read the entire page →
From page 55... ... 55 to another given an action is taken. All of these parameters are populated by default based on what asset is selected in the input page, so one would set these only if developing a new model. Read the entire page →
From page 56... ... 56 • Recommend Action by Condition State – action which, if taken in the specified condition, minimizes life cycle costs. Default actions include doing nothing, rehabilitation and replacement; • Unit Agency Cost – unit cost of the recommended action; and • PI – PI value for performing the recommended action in the specified condition. Read the entire page →
From page 57... ... 57 Buses XYZ Transit's bus fleet is assumed to be similar to that of the Port Authority of Allegheny County. The fleet consists of 14 subfleets together totaling 876 forty-foot buses. Read the entire page →
From page 58... ... 58 corresponding linear trend line. In the period from 2005 to 2009, MDBF declined from approximately 11,000 to 6,000 miles. Read the entire page →
From page 59... ... 59 mutually exclusive, although in practice most of the projects can be subdivided between years. 5.4.3 Define Scenarios The next step is to define scenarios for analysis and characterize the results for each scenario. Read the entire page →
From page 60... ... 60 vehicle delay would increase by 26%, and track delay would increase by 28%. Also, escalator availability would decline and the percentage of vehicles in poor condition would increase dramatically. Read the entire page →
From page 61... ... 61 project ranked lower initially is programmed before a higherranked project because its PI grows faster. This is the case for replacement of Light Rail Vehicle Fleet A Read the entire page →

From page 44...

... 44 S E C T I O N 5 5.1 Introduction This section describes tools and approaches for applying the framework described in Section 4 to evaluating rehabilitation and replacement for specific types of transit assets. Section 5.2 summarizes the recommended analytical approach to prioritize rehabilitation and replacement alternatives and evaluating rehabilitation and replacement of existing transit assets, with guidance on models for specific asset types.