Not really sure what you are asking but in the train purchase set up a new train is automatically at a starting point.  If you want to change that starting point you need to put in a 2nd station and click on it as a starting point.  I do this alot when I have two big stations such as Detroit and Chicago.  I make up a train from D to C then purchase another train and the last one purchased comes up and I reverse the starting location.  If you are not connecting your track then you must dump the unreachable station when purchasing a train and click on a new starting location on your map.  Hope this helps. FR