This report presents the results of bus simulation studies which determined the effects of various design and operating parameters on bus fuel economy and performance. The bus components are first described in terms of how they are modeled. Then a variation of each component is performed and the resulting fuel economy and performance are presented as sensitivities and tradeoffs. Relative fuel consumption estimated by the HEVSIM Simulation Program and measured in track tests was shown to compare within ± 1 percent in six of nine cases. Explanations are offered in cases where the variation was slightly greater than the ± 1 percent band allowed by the SAE Type II J1321 test procedures.