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This paper presents model-based predictions of the performance of diesel, compressed natural gas (CNG), and hybrid buses on bus routes in the City of San Francisco. The bus route details were obtained by recording time-series measurements of speed and grade during actual runs of buses on the city streets under different traffic conditions. The transit buses' physical and mechanical characteristics were obtained from manufacturers' data and chassis dynamometer testing of the buses on different city cycles. Both the bus routes and the bus performance characteristics were put into the simulation package ADVISOR from the National Renewal Energy Laboratory (NREL). The most extreme results were for the San Francisco routes that have high grades. The high grades cause performance and emissions problems for both the diesel and CNG buses relative to the hybrid bus.