Was für ein cleveres Projekt!

No really you can be quite proud of yourself for building such a well thought out and fun system. The game works great and it simply feels fun to lay down tracks. 
If I had to voice a criticism it would probably concern the UI-Design; the game is not only very reliant on text, but some parts of the track-placing-mechanics were hard to understand at first and felt finicky. 
Disregarding my minor nitpicks, the overall execution is very strong and I could easily imagine this idea to be developed further into some truly mind-blowing puzzles. 

Music & SFX

The music and sound design is quite pleasing, which is a lot more for puzzle games than some might think, but when you are stuck in a level for minutes on end you tend to notice if the music doesn't drive you insane. 

Visuals 

A very functional design—It could maybe be improved into a similar vein of mini metro, but the design right now is perfect for what the game needs to convey. 
Disregarding my previous gripes with the UI it's also quite functional and mostly clear. 

Puzzle design 
Right now it mostly feels like tutorial, but I did enjoy it quite a lot.

I would love to see what you cook up next!