The National Highway Traffic Safety Administration (NHTSA) estimates that vehicle to vehicle communication could prevent 615,000 vehicle crashes and save 1,366 lives. Low latency (less than 50ms) high speed wireless networks can provide signaling between vehicles and infrastructure. Yet, while the benefits of V2V seem clear, the technological approach is still under debate and center primarily on the appropriate utilization of sub6 spectrum (5.850-5.925GHz).
Two approaches have largely been explored - 3GPP LTE V2X (PC5 side link) and DSRC (802.11p). Both of these approaches utilize the 5.9GHz band. DSRC had been the de facto approach with spectrum already allocated several years ago, but now, with the growth of 5G there is a renewed debate on how best to utilize spectrum for V2V communication.
It does seem that, at least for a while, the two technologies may be able to co-exist. The FCC voted in December 2019 to split the spectrum to allow for the upper 20MHz of the band to be dedicated to cellular based V2X communication. Nevertheless, 45MHz is allocated to unlicensed communication limiting some potential of cellular V2X but providing a use case for Wi-Fi. Certain devices may be dual-homed allowing for communication across Wi-Fi and cellular. In other instances, some types of messages may be Wi-Fi based and others may be cellular based.
5G - 5G has evolved to provide two modes of communication, one based on licensed communication to a cellular network and a separate direct peer to peer method. A main drawback of 5G had been the time for infrastructure to be built. We are already seeing handsets with 5G capabilities and it is likely that the next few years 5G network will be built out substantially. If the penetration of 5G continues to increase, the likelihood of vehicles in the vicinity of each other having a capable 5G v2v system is set to increase substantially thereby making 5G a compelling platform.
The 5GAA association, contends that given the higher likelihood of penetration and radio link performance of 5G, cellular v2x is a more compelling platform. The chart below depicts the packet reception ratio for LTE V2X and 802.11p performance. The full report can be found here. According to their modeling, the drop off in performance for 802.11p is even more substantial in urban environments.