To meet the ever increasing demand of mobile data traffic, 5G enabling technologies are proposed in vehicular networks. Network densification is one of the key 5G technologies for large user throughput and traffic capacity, but there is a great challenge to serve numerous vehicular neighbors. According to observations from a real dataset of vehicles, we discover vehicular neighbor groups (VNGs) consisting of groups of vehicular neighbors. VNGs are crucial to enrich and enhance various services in 5G networks through efficient management. Therefore, we propose 5G-enabled software defined vehicular networks (5G-SDVNs), where software defined networking is exploited to dynamically manage VNGs in 5G and vehicular environment. Furthermore, we leverage mobile edge computing to strengthen network control of 5G-SDVN. By combining software defined networking with mobile edge computing, a programmable, flexible, and controllable network architecture is introduced for 5G-SDVN. The architecture simplifies network management, improves resource utilization, and achieves sustainable network development. We use the universal plug-andplay standard to enable scalable VNG networking. A case study of vehicular cloud computing highlights the advantages of 5G-SDVN. Finally, we also identify and discuss open issues in 5G-SDVN.