i think maybe you only have excess for the quest you can do there after so story of episode 18.
i cant get in aswell although ive done the quest alrdy.
so maybe its just for the quest you can get there
this is a entirely diffrent quest your looking at.
for the railnet part you have to go north west ish-
(if you enter from the city. and enter the first house in the wasteland , you have to go north west from there)