Concerns for spectrum congestion have spurred extensive research efforts on efficient spectrum management. Therefore, devising schemes for spectrum sharing between radar and wireless communication systems has become an important area of research. Joint communications-radar (JCR) system is among the several approaches proposed to achieve this objective. In JCR systems, additional components and processes are added to an existing standardized communication platform to enable radar functions. Moreover, the communication waveform is used as an integrated JCR waveform, i.e., the same signal is used to communicate information to a receiver and to perform radar detection and estimation operations for a nearby target. The most common application of JCR systems is found in vehicle-to-vehicle (V2V) communication scenario. In this article, an overview of the spectrum sharing methods is presented, with focus on JCR systems in automotive applications. We first review the recent works on IEEE 802.11p- and IEEE 802.11ad-based radars. A basic description of the modeling of JCR system and channels is presented, followed by discussions on main components and processes employed in various JCR systems. Mainly, we are interested in how the radar detection and estimation functions are performed in conjunction with the communication receiver functions with minimal alterations in the existing system. At the end of the paper, some performance trade-offs between the communication and radar sub-systems are also discussed.