Journey times are often traded off to improve capacity. Suppose we magically found a way to fit 5 times more people on one train, and needed way less capacity than we have. What projects, any scale, would you suggest to improve journey times instead?
I think that misrepresents the trade-off.
The problem is more likely around
network capacity rather than
train capacity.
An example of this is the line from Doncaster to Leeds, used by LNER intercity services and Northern stopping services. It has a linespeed of 100mph – there would be no point in speeding it up to 125mph because with a half-hourly intercity service and a half-hourly stopping service that takes 15–20 minutes longer (yes, I'm simplifying things to illustrate the point) if you ran the LNER services faster then they would just catch up with the stopping services and then have to slow down.
It doesn't matter what
capacity you offer on each train, you still want to run both routes half-hourly to provide a convenient service, so it doesn't matter how many more people you can fit in each train, you're not going to be removing any trains from the network and so you're not going to be getting any longer gaps that would make it worthwhile speeding up the fast trains.
