Okay, so there was another question like this but not quite the same (although the same answer may or may not cover both)...
How are junctions going to work, if at all?
Will it be abstracted, allowing carts to switch direction freely at any point where more than one rail intersect? Or only at 'stop' tiles? In either case, how will runaway carts coming up to the head of a 'T-junction' from the tail be handled? Will they just derail at that point, or will they be diverted? In the case of the latter, will the direction be random or constant?
Or will there be splits like on IRL rail lines, where carts coming from one direction are sent in only one of two (or three!) possible directions? If so, what would happen to carts coming up a secondary rail when its not the one presently being diverted to?
Concerning stops, would they work more like turntables, railheads, or just ordinary stretches of track? Would it be possible to link a lever/pressure plate to them and disable them, or to power them and launch carts into the system? Or do the dwarves have to manually send carts off again, unless one designed a system where an empty cart bumps the full one out of the stop?
Lastly: as for the carts themselves, would it be possible to use them as mobile stockpiles? By that I mean if I filled up some carts with stone and sent them down a dead-end rail to my masons' shops, would they take their stone directly from the carts or must I get some haulers to unload them first?