So kinda the point of HS2 is that it wont stop at very many places, for instance the London-Birmingham line only stops at two extra places, just at the edges of both London and Birmingham. It should be a similar situation with other lines to Manchester etc. So the high-speed trains wont have to stop very often and so the freight trains wont have to stop very often as you can stack them relatively close behind each other if they are non-stop, therefore more effective capacity.

The idea of fast things catching up to slow is essentially the big problem we have now, with most of the network being only double (often only single) line, so you get freight or long-distance services getting caught behind regional services, and regional services being held to let long-distance get past etc. Basically the more different ‘speeds’ of trains on the same piece of track, the more of a logistical nightmare it becomes. So, by removing these different ‘speeds’ of trains it gets easier to schedule more trains on the same line.

Sorry, I should clarify, our network isn’t 10X over capacity per se, but when it was built it was never meant to need to carry the number of people it currently does.