I've just run into a fully 6-sided rail tile, and am unable to place it anywhere.
I suppose being unable to place the current tile is an alternate means of a game over? Except the game as it stands doesn't seem to recognize this as an end-state. It'd be nice to have a recognition of that.
It'd also be nice to have both a freeform mode and a semi-constrained mode, where you have goals but the tile count is less imposing and/or you could, for instance, switch out the current tile for a saved tile perhaps, a la Tetris, or else switch with the very next tile in the stack.
I find that I want to design a 'pretty' landscape, but to do list considerations are often forcing me to make ugly choices like intentionally stacking field/city/field/city lines out on their own just to get enough tiles to keep going.
Very neat little game, I look forward to seeing it develop further.