Non-safety applications such as autonomous driving and crowd sensing require substantial data transmission, exacerbating the scarcity of spectrum resources in the Internet of Vehicles (IoV). To mitigate this issue, cognitive radio-assisted IoV (CIoV) has attracted increasing attention. Despite extensive research addressing various challenges in CIoV networks, securing additional spectrum opportunities continues to be a key obstacle. This paper explores whether the signal-blocking effect of viaducts can provide additional spectrum opportunities for vehicular secondary users (SUs) in CIoV networks. First, we classify primary user (PU) regions into three types based on signal reception characteristics and introduce a novel parametric geometric model to estimate the geometric boundaries of each region. Next, we use a dual-path propagation model to figure out the reflection and penetration coefficients for both vertical and horizontal polarizations. This helps us figure out how much interference power there is between the SU transmitter (SU-Tx) and the PU receiver (PU-Rx). Finally, we use real-world parameters to conduct two case studies, showing that SUs’ transmissions do not cause harmful interference to PUs when operating at specific heights. We also provide a comprehensive analysis of how various parameters influence the interference from SU-Tx to PU-Rx, using detailed numerical results.