With its fine immunity to multipath fading, ultra-wideband (UWB) is considered to be a potential technique in constructing intravehicle wireless sensor networks. In the UWB literature, extensive measuring and modeling work have been done for indoor or outdoor propagation, but very few measurements were performed in intravehicle environments. This paper reports our effort in measuring and modeling the UWB propagation channel in commercial vehicle environment. In our experiment, channel sounding is performed in time domain for two environments. In one environment, the transmitting and the receiving antennas are put beneath the chassis. In another environment, both antennas are located inside the engine compartment. It is observed that paths arrive in clusters in the latter environment but such clustering phenomenon does not exist in the former case. Different multipath models are used to describe the two different propagation channels. For the engine compartment environment, we describe the multipath propagation with the classical S-V model. And for the chassis environment, the channel impulse response is just represented as the sum of multiple paths. Observation reveals that the power delay profile (PDP) in this environment does not start with a sharp maximum but has a rising edge. A modified S-V PDP model is used to account for this rising edge. Based on the analysis of the measured data, channel model parameters are extracted for both environments.