And at road crossings and passing loops and so on. Really long trains are a fairly significant logistical challenge.

Yeah, I would rather go with smaller, but automated trains. But in germany for example this would mean, basically changing everything installed electronically there already is.

The problem with trains in Germany is not high tech automation it is the aggressive cost-cutting that removed a lot of redundancy and stability, so now it is a worse service in quality and reliability

Well, it is one of the problem. Recently new tech was installed - but not at all with the idea of automatisation in mind. Apart from that I know, I often had the fun adventure of not knowing will I catch the last connection, or not.

Sure, I'm dramatically oversimplifying, but I think my point still stands: putting it another way, trains have an ability to accommodate travelers in a way that nothing else -- planes, cars, buses, etc. -- can even approach. It wouldn't be as easy as I'm making it out to be, but it also doesn't seem (in the larger picture) to be particularly challenging either.

And you're right, you'd probably have to designate a section of the train as the "getting on and off" bit, and make it easy for people to move from car to car.