Level 5 integrated automated vehicle integration is what is needed. It would have been nice to set aside bandwidth for the roadway to vehicle, and vehicle to vehicle communications, that would make up that 5th level of system integration. Level 5 has overlapping, visual, lidar/radar ranging inputs, that would be confirmed by information from say the traffic signal, all confirming with each input, that signal is truly "green" or "red" and react safely within the information. Some manufacturer's like to "hype" their "auto-pilot" (barely maybe level "2.5"???) system now known best for the spectacular ways some users have found to record their deaths live streaming, while using it....

Choo-choo's being a "closed system" compared to a roadway network is theoretically more "programmable". Unfortunately, the costly and somewhat stilted choices made for the system architecture used for PTC, has left me just a bit underwhelmed and unimpressed. Having actual certification in systems analysis user needs for ITS systems, and having taught a class or two for FTA and FHWA in how to define system "user needs", I was underwhelmed and unimpressed by FRA's process. And, then there is the problem of operational environment, which you mention, and which presents another set of costly challenges to contain and control.