@quixoticgeek @forestpines @http @julf @marcas @tml @SteveJonesnono1 Bear in mind that tracks have a hard capacity limit—more than one train can't run within the same signal block (it's a safety thing) so they need to be spaced apart. Fast trains also take further to stop, so you can have fewer of them per unit track length. So "run trains more frequently" actually implies "build more tracks". And 5% of your track network needs replacing every year. So this drives up fixed costs.
@cstross
Going with Edinburgh to London as an example: there's plenty of capacity to run more trains between Edinburgh and Newcastle...except that Newcastle Central Station itself is pretty close to capacity
Further south the main line basically gets more and more traffic the further south you go, until it's also at full capacity south of Hitchin (where the Cambridge & King's Lynn trains join the main line)
@quixoticgeek @http @julf @marcas @tml @SteveJonesnono1