Love this game so much and I'd like to suggest a few ideas:

1. Let us move existing objects instead of deleting them and add them back.
2. Add more double-track pieces, especially junctions
3. Let us place train wagons without an engine.
4. Let us change the length of a bridge for a few tiles. It looked awkward to add single bridge pieces to fill the gap which has different style to the main bridge.
5 Let us build bridges over tracks, including both train bridges and footbridges.
6. Add river pieces so we can connect to waterfalls.

Thanks for your kind attentions.