This is my Ludum Dare 29 entry. The theme was Beneath the Surface.
I didn't have too much time for this, so the whole game was fully done (from idea to submission) in close to 10 hours. I don't think this impacted the implementation a lot, but it meant I had to go forward with the first idea that we had. (Which was, in fact, my girlfriend's).
Interesting implementation point here was using a Voronoi diagram to decide which station connects to each other (all rails are, in fact, perpendicular to edges of the Voronoi cells of the station).
I've spend most of the time trying to get some user input that didn't suck. I experimented with the car automatically running, with break only mode, with different speeds, etc. Ultimately, being able to fully control forward/backwards was the most fulfilling choice.
I also had implemented some passenger mode, where you could see little passengers on the train and deliver them to each station, but it was just very distracting and not fun. Finally, I also had plans for different types of missions, but then I realized they are all variations of "go to a particular station", so I cut those out too.