You can connect the train tracks to waypoints and then move those around to create your track. Waypoints are these green spheres that only appear in Edit mode. You can use them to create paths for NPC's, Moving Platforms, Wave Spawners, and in this case extend train tracks.
So put down your train track and connect the green ball in the front to a new waypoint you set down somewhere in front of it. Then connect as many waypoints as you'd like from there and youll see the track update . When're done, connect the last one to the red ball to complete the loop. When you want to ride just look at the track and hit 'e'.
Hopefully that makes sense. If not I can post a screenshot. Thanks for the feedback. I'll be sure to include more about the tracks in a tutorial!