You could (I would even say those would be seperate stations then, even if they share the building), but virtually no station is build that way and it would cos

You could (I would even say those would be seperate stations then, even if they share the building), but virtually no station is build that way and it would cost quite a lot of money to "untangle" the tracks. Probably too much money. Doesn't help that most high-speed trains drive on a mix of seperate high-speed tracks and normal tracks shared with regional and freight trains, making complete seperation impossible. :/