Fully automated freight rail is not possible with the infrastructure and technology we currently have unless the rail companies accept insane risk.
For example, if one of the locomotive engines stops working and the train must stop, you need to keep the brake lines pressurized. For some archaic reason they fail open instead of closed, so you have to keep the engines running at all times. Otherwise, you need to send a guy out to manually apply the emergency brakes. This was part of the cause of the Lac-Mégantic disaster.
So it's not impossible, but there's zero chance that NS or CSX would ever invest $MM to upgrade the brakes on all their trains to let them run automated. But the real crux of it is that they'd be responsible for any disaster, and their go-to strategy is to just blame whoever happened to be in the cab that night.
I think most of it is legacy. Trains have been around for a long time, and changing something on tens of thousands of locomotives and millions of train cars would be very expensive and complicated. Most systems now have a reserve tank on each car that holds a certain pressure, and the braking signal is sent by reducing the pressure from the main unit. But it's still not nearly as safe as automotive air breaks that fail closed, since eventually all the air will leak out of the tanks.
For example, if one of the locomotive engines stops working and the train must stop, you need to keep the brake lines pressurized. For some archaic reason they fail open instead of closed, so you have to keep the engines running at all times. Otherwise, you need to send a guy out to manually apply the emergency brakes. This was part of the cause of the Lac-Mégantic disaster.
So it's not impossible, but there's zero chance that NS or CSX would ever invest $MM to upgrade the brakes on all their trains to let them run automated. But the real crux of it is that they'd be responsible for any disaster, and their go-to strategy is to just blame whoever happened to be in the cab that night.
https://en.wikipedia.org/wiki/Lac-M%C3%A9gantic_rail_disaste...