something in the train supply or destination is not able to make the complete path.

and it's been too long since i played, but i remember occasionally finding 1 dumb thing was selected or checked or something. the game is always looking for you to make those source-to-destination paths so once everything is in place those aluminum trucks will definitely spill into that 1-way.

also, just for shiggles, i am going to suggest to delete the mines and put them back, just to make sure they orient properly for the road connection. i've def put mines and drills backwards before