Thanks for sharing this eh. I love the gameplay and I think you can build this out into a fine game if you decide to continue. I enjoyed the logistics of just building more and more. Since victory is about throughput (the first derivative) I do not think a money (the second derivative) makes sense as a mechanic.
I think more visual polish, like cars filling with goods or buildings showing icons for what they accept, would be the first thing I would do next. Then if you feel more mechanics are needed I would focus on trains changing layers which would multiply the chaos, and or more catalysts which encourage more connections.
Right now the main "currency" is build-able space. Focus on mechanics which use that currency in new ways.
For teaching the player maybe have a starting scenario where some tracks and trains are already built. This would allow you to teach techniques like crossing track or catalysts without text. It could also allow you to make scenarios as content.
Please consider terrain or obstacles. All these should give room for you to make challenging levels which are more than just pure throughput tests.
Daniel