It is interesting to consider Tokyo station in Japan. There, at the heart of a huge interchange complex, the two separate Shinkansen networks meet and both terminate right next to each other from opposite directions. Despite both being standard gauge there is no physical track connection whatsoever between them, not even an emergency or engineering link. There's a lot of history behind that separation, and it persists today partly because of different ownership and a different frequency of AC power supply. The arrangement completely prevents delays from one network propagating into the other clearly, and recognises that the majority of travellers on both are heading for the greater Tokyo area, so either interchange with other services at Tokyo station itself or at one of the other major satellite hubs called at further out. That the two networks share a central station however means connections between them are still very easy, and with Tokyo being roughly around the midpoint of the long thin archipelago, that offers some attractive long-distance journey opportunities.