Integrated Sensing and Communication (ISAC) is a critical technology in vehicular networks, which combines the sensing and communication capabilities in one system. Due to limited resources such as spectrum and transmit power, one essential problem lies in the study of ISAC-based vehicular networks is the performance trade-off between sensing and communication. In this paper, by applying tools from stochastic geometry, we first model the vehicular network as the Cox process driven by a Poisson line process (PLP). Then, we derive the detection probability of the sensing module and the coverage probability of the communication module, respectively. We further capture the respective performance trade-off between sensing and communication under the bandwidth budget based on the derived analytical results. Finally, extensive simulations are conducted to verify the accuracy of our derivations. This research is essential for optimizing resource allocation and improving service quality within ISAC in vehicular networks. By focusing on the integration of sensing and communication capabilities, we aim to advance the development of smarter vehicular networks that can better meet the needs of users.