Great little game! Excited to see it fleshed out more.
Very minor bug, but I got an error pop-up when using the "Exit" button from the menu on the build screen (pasted below). I wasn't able to replicate it, so it may be random, or related to my habit of sometimes clicking with both mouse buttons at once (this breaks way more in-development games than you'd think!).
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ERROR in action number 1
of Step Event0 for object obj_game_controller:
Variable obj_train.total_width(102410, -2147483648) not set before reading it.
at gml_Object_obj_game_controller_Step_0
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gml_Object_obj_game_controller_Step_0 (line -1)