2 Vehicle technologies and bus fleet replacement 3 optimization : problem properties and sensitivity 4 analysis utilizing real - world data 5

8 Abstract This research presents a bus fleet replacement optimization model to 9 analyze vehicle replacement decisions when there are competing technologies. The 10 focus of the paper is on sensitivity analysis. Model properties that are useful for 11 sensitive analysis are derived and applied utilizing real-world data from King 12 County (Seattle) transit agency. Two distinct technologies, diesel hybrid and con13 ventional diesel vehicles, are studied. Key variables affecting optimal bus type and 14 replacement age are analyzed. Breakeven values and elasticity values are estimated. 15 Results indicate that a government purchase cost subsidy has the highest impact on 16 optimal replacement periods and total net cost. Maintenance costs affect the optimal 17 replacement age but are unlikely to change the optimal vehicle type. Greenhouse 18 gas emissions costs are not significant and affect neither bus type nor replacement 19 age. 20 21