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Transportation -- Oregon -- Portland Metropolitan Area -- Planning, Transportation -- Planning


The purpose of this study was to gain a better understanding of how equipment replacement decisions are supported with data collection and quantitative models at state DOTs, and to determine if models found in the research literature offer any better decision support when applied to realistic fleet usage and cost data. This study also addressed the current state of equipment replacement at state DOTs with respect to using measurable “green” criteria in replacement decisions, and the development of new quantitative replacement models utilizing such criteria. The responses from 25 state DOTs indicates that there is little consistency in the criteria used by state DOTs to support replacement decisions and the way that these criteria are used. There are also no measurable “green” criteria utilized. However, most state DOTs maintain an information system where cost and usage data is recorded, stored, and utilized as part of the replacement process. To investigate if a particular modeling approach offers better performance than the variety of approaches used in practice, a simulation study was conducted. Simulation models were used to evaluate the effectiveness of replacement models for prioritizing equipment replacement. The models evaluated come from the research literature and were compared to a simple replacement model that is similar to those used by state DOTs. Results indicate that the simple models used in practice provide similar results to the best model from the research literature.


This is the final report, OTREC-RR-11-03, from the NITC program of TREC at Portland State University, and can be found online at:



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Green_Vehicle_Fleets.pdf (473 kB)
Supplemental Case Study