Question On Logic Gates
Digital circuits can represent yes or no. Here I am defining an output of '1' can means the given station can accept a given train. The question is vague, but I'm assuming that each station can only fit one train in it at a time. 

So let's breakdown your problem into inputs and outputs. With those inputs and outputs we can get a truth table, and by extension a logic circuit. One input can be if a train is 'up' or 'down'. One output can be if station 1 can accept a train or not. If a train is down, we know that station 1 can not accept it. So on your input output table, if the input train is 'down' (let's call that 0), the output for station 1 is always no entry ('0'). 

So now we can add some more inputs. If the train is 'up' (let's call that 1), depending on the if the station is empty or full it may be either 'no entry' (0) or 'entry' (1). So we can make a 'station 1 empty' signal. If station 1 is empty, and the train is 'up', station 1 can accept the train (output a 1). If the station is full, you can fit another train, so the station can't accept the train (output a 0). 

Repeat this process for the other stations and organize it into a table. Once you do that it's just a matter of truth table -> digital circuit, which I am positive that has been answered thoroughly on this site and others.