Existing bus fuel consumption models produce a bang–bang type of control, implying that drivers would have to either accelerate at full throttle or brake at full braking in order to minimize their fuel consumption levels. This is obviously not correct. The paper is intended to enhance bus fuel consumption modeling by circumventing the bang–bang control problem using the Virginia Tech Comprehensive Power-based Fuel consumption Model (VT-CPFM) framework. The model is calibrated for a series of diesel-powered buses using in-field second-by-second data because of a lack of publicly available bus fuel economy data. The results reveal that the bus fuel consumption rate is concave as a function of vehicle power instead of convex, as was the case with light duty vehicles. The model is calibrated for an entire bus series and demonstrated to accurately capture the fuel consumption behavior of each individual bus within its series. Furthermore, the model estimates are demonstrated to be consistent with in-field measurements. The optimum fuel economy cruising speeds range between 40 and 50 km/h, which is slightly lower than that for gasoline-powered light duty vehicles (60–80 km/h). Finally, the model is demonstrated to capture transient fuel consumption behavior better than the Motor Vehicle Emission Simulator (MOVES) and produces a better fit to field measurements compared to the Comprehensive Modal Emission Model (CMEM).