Along a fourteen-kilometre stretch of track north of Dublin, Ireland is confronting a truth familiar to growing nations: infrastructure built for one era cannot quietly absorb the ambitions of another. Irish Rail's FourNorth project — a billion-euro plan to double the tracks between Connolly station and Malahide — is less a response to a single crisis than a reckoning with decades of deferred capacity, now made urgent by the simple act of running more trains between two cities that share a complicated history and a common future.