Unfortunately there's also still no agreement on what 5G will actually be, what technologies it will entail, or how it will be deployed. Of course, since none of this is defined yet, there are also no guarantees on what performance will be achievable in practice.
The industry will need to solve this issue long before 5G is widespread. The solution will likely involve DSRC, C-V2X, or LTE-V/LTE Direct, which are tailored for the vehicular communication use case (involving both vehicle-to-vehicle [V2V] and vehicle-to-infrastructure [V2I]). It's unlikely a single technology will be able to handle all the challenges of a V2X scenario (highly mobile nodes, congestion, low SNR, requirements for sub-millisecond connection times), and so a second connection management layer will have to be built on top of multiple existing PHYs to enable simultaneous low-latency, high-throughput, and secure communications.
(Note that the linked article is actually about in-vehicle communication, however.)