Of course we can automate trains. I'm working in a research project doing that right now on a rail track between the Netherlands and Germany. It's quite a bit of work but I don't see any fundamental issues.
https://www.youtube.com/watch?v=hf5iBbmas2w
... until it isn't:
https://www.youtube.com/watch?v=Ec8Yx-Mp-5s
Linked more for your interest than to make any point - the derailmant issues in the second link weren't directly linked to automation, but we do have big train sets here in W.Australia.