Key Variables Affecting Decisions of Bus Replacement Age and Total Costs

Transportation Research Record: Journal of the Transportation Research Board, No. 2274, Transportation Research Board of the National Academies, Washington, D.C., 2012, pp. 109–113. DOI: 10.3141/2274-12 Department of Civil and Environmental Engineering, Portland State University, P.O. Box 751, Portland, OR 97207-0751. Corresponding author: M. Figliozzi, [email protected]. A formal optimization model dealing with machine replacement problems was first introduced in the 1950s (2). Since then, many researchers have analyzed replacement problems in a wide range of fleet types, including transit and police fleets (3, 4). Some researchers have added budget constraints and even integrated vehiclemanufacturing waste factors in an automobile life-cycle analysis (5, 6). Despite the great uncertainty associated with financial variables and forecasts, all the models mentioned have been deterministic. Little or no attention has been given to sensitivity analysis. Researchers have looked at cost trends in transit agencies by tracking fleet costs over time. Long-term cost data of bus fleets have consistently shown that operations and maintenance (O&M) costs rise with age (7–9). Other research has shown the value of modeling preventative and unexpected repair costs over time and their impact on the optimal bus replacement age (10, 11). The cost of replacing, refabricating, and rehabilitating buses has been a focus of research by Khasnabis and colleagues, as well as the optimal allocation of FTA funds among transit agencies (12–14). Unlike the present work, previous studies have evaluated fleet costs and their impact on replacement age, but they have not modeled all the relevant factors that vary as a function of bus age (e.g., utilization and fuel consumption). A comprehensive literature review on the factors affecting bus replacement modeling can be found in Boudart (15).