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7The literature review involved a search of major sources includ- ing transit agency websites, TRB proceedings and publications, and APTA publications. The literature search was conducted using web and Transportation Research Information Services (TRIS) search engines. The literature search focused on identifying technical methods used for effective transit asset management. As mentioned in chapter one, these methods can be used to produce an estimate of the funding required to address asset replacement and rehabilitation needs. The methods can also help set and prioritize the programming of replace- ment and rehabilitation projects when available funding is constrained. The literature review found a large number of publications that discussed the importance of maintaining transit assets in SGR. Generally, the major focus of these articles was that the condition of transit assets has been declining through under- investment and that increased funding is needed to reverse this decline. These publications, however, did not discuss or describe the technical methods that might be used for more effective transit asset management. The literature on technical methods used for transit asset management is limited. Eight articles, papers, or reports were identified and judged important to this synthesis project. The publications are cited in the References and summarized in the Annotated Bibliography found in Appendix D. Although the literature is limited, the review of the relevant sources suggests how the technical methods may advance in the coming years and become more comprehensive and sophisticated. The key advances may come in several areas including the definition used for SGR, the asset costs consid- ered in the analyses, and the use of scenario testing. MEASURE OF THE STATE OF GOOD REPAIR The conventional approach for defining assets being in SGR is that the assets are replaced before the end of their useful life. Examples of these definitions are 12 years for buses, 25 years for rail cars, and 50 years for stations. Often, these definitions are based on federal grant require- ments that only permit federal funding to be used for asset replacements when the assets have reached minimum ages. Recent and more detailed approaches recognize that, in practice, the need to replace an asset is related not only to age, but to other factors as well, such as intensity of use (e.g., miles), level of preventive maintenance, and climate. There- fore, two identical assets may be scheduled for replacement at different ages based on the intensities of their use and their respective levels of maintenance. The approach used by the FTA in its Transit Economic Requirement Model (TERM) is an excellent example of this approach (Laver 2009). It simulates the full life and decay of all transit assets based on factors such as asset use (e.g., miles), annual maintenance, and age. Empirically derived decay curves are used to determine when assets should be replaced. These curves are based on detailed asset condition inventories that used a five-point scale (1 = poor condition, 5 = excellent condition). An asset is replaced when its condi- tion falls below 2.5. Another advance is suggested by the approach developed in Illinois for determining when buses should be replaced (Booz Allen Hamilton 2003). A minimum cost replacement strategy was used to minimize total life-cycle costs. These costs were allocated over the life of a vehicle on a per mile basis. The pur- chase and rehabilitation costs per mile decline over the life of the vehicle. In contrast, operating and maintenance costs per mile tend to increase as a vehicle ages. When these divergent unit cost trends are combined to produce a total life-cycle cost curve, a minimum unit cost and its corresponding lifetime mileage can be determined and used as the replacement point. ASSET COSTS CONSIDERED A common public view is that good transit asset management will be achieved when there is sufficient funding to replace or rehabilitate assets at the end of their useful lives. Therefore, the task is to determine the needed replacement and renewal funding. This approach ignores the issue that mid-life renewals often are needed to ensure that assets reach their useful life. Exam- ples of these mid-life renewals include the replacement of engines and transmissions for buses, heating and roofs for sta- tions, and traction motors and assemblies for rail cars. More comprehensive approaches recognize the need to include these mid-life renewals (Yoder and Delaurentis 2003; CHAPTER TWO LITERATURE REVIEW
McCollom 2006; DâAlessandro et al. 2009; Laver 2009) as part of good asset management analysis. However, there is limited information in the literature about how these mid-life actions should be defined for all asset types. SCENARIO TESTING Most of the applications documented in the literature provided estimates of the capital funding needed to bring the assets to, and maintain the assets at, SGR. This might be termed âideal SGR funding.â However, in many communities, funding is limited. Deci- sion makers would like to know the consequences of provid- ing less than ideal funding. The Boston methodology (McCollom 2006; DâAlessandro et al. 2009) was the only one identified that included the abil- ity to prioritize the funding of specific asset renewal or replace- ment projects in constrained funding environments. It uses a weighting scheme that relies on several factors, such as rider- ship impact, replacement costs, and impact on operations, to determine funding priorities. The consequences include a sum- 8 mary of asset actions (replacement or mid-life maintenance) funded on-time, later than scheduled, or not at all, and changes in the backlog of actions throughout an analysis period. The limitation of the Boston approach (McCollom 2006; DâAlessandro et al. 2009) is that the consequences are related to the successful completion of desired programming actions. It does not estimate impacts of underinvestment on operating costs, service reliability, safety, and passenger usage. SUMMARY The limited availability of literature on this topic suggests that the active use of asset management systems for more than data collection and manipulation of asset inventory data is not com- mon. As the state of the industry matures, it is reasonable to expect more reports on this subject. Although the literature is limited, it provides a strong indi- cation of where methodical improvements will be made. Sig- nificant advances were found in the definition used for SGR and the asset costs considered in the analyses. More work is needed in forecasting the consequences of underinvestment.
