  Vehicle-to-Everything (V2X) communication is expected to accomplish a
long-standing goal of the Connected and Autonomous Vehicle (CAV) community to
bring connected vehicles to roads on a large scale. A major challenge, and
perhaps the biggest hurdle on the path towards this goal is the scalability
issues associated with it, especially when vehicular safety is concerned. As a
major stakeholder, 3rd Generation Partnership Project (3GPP) based Cellular V2X
(C-V2X) community has long been trying to research on whether vehicular
networks are able to support the safety-critical applications in high-density
vehicular scenarios. This paper attempts to answer this by first presenting an
overview on the scalability challenges faced by 3GPP Release 14 Long Term
Evolution C-V2X (LTE-V2X) using the PC5 sidelink interface for low and
heavy-density traffic scenarios. Next, it demonstrates a series of solutions
that address network congestion, packet losses and other scalability issues
associated with LTE-V2X to enable this communication technology for commercial
deployment. In addition, a brief survey is provided into 3GPP Release 16 5G New
Radio V2X (NR-V2X) that utilizes the NR sidelink interface and works as an
evolution of C-V2X towards better performance for V2X communications including
new enhanced V2X (eV2X) scenarios that possess ultra-low-latency and
high-reliability requirements.
