[Aachen]

I will admit to having only read the first point of the long post, so I'll just respond to that:

> It doesn't take that many different operators before you start running into capacity limits of the network

Don't get this. If there is that much demand, then clearly it makes sense to build out the system? More rails, higher speed, and/or better bypasses for trains that need to stop at each station for example.

It's usually a hard question to predict where public or investment money is best spent, but this situation seems like it would be quite clear.

[iggldiggl]

Unfortunately these days building out capacity is usually neither cheap nor fast, so it's not uncommon to get stuck in some sort of intermediate twilight zone where you have somewhat too many trains for too little tracks, but not so many that building out additional infrastructure is clearly warranted (and even when it is warranted, planning and construction will unfortunately nowadays take years to decades, and what do you do until then?).

Open access operators also often start running only a few trains per day – building additional expensive infrastructure for just a few trains per day might not be worth it, but conversely a few trains per day are potentially already more than enough to upset an exiting regular interval timetable and timed connections.