The articles in this special section focus on software-defined radio in vehicular networks. Due to the random vehicle mobility and varying communication environment, an integrated vehicular network comprising heterogeneous access technologies (DSRC, WiFi, 4G/LTE, 5G, etc.) will be indispensable to provide ubiquitous mobile coverage. Although heterogeneous networking has been extensively studied in different contexts, the salient features of vehicular communications, fast mobility) have brought new challenges and led to fundamental and interesting research issues, such as how to flexibly configure and efficiently conduct resource allocation, how to enable interoperation among multiple coexisting networks, and how to effectively accommodate a large number of traveling users with various kinds of smart devices.