From my own metaphorical doorsteps, when it comes to having a conveyor system that loops back on itself in several places, I would prefer the game to give priority to whichever car has had more done to it already (and so will leave the system sooner, or else be sent down a path taking it out of whatever the other car has yet to experience). Its not outside the realm of possibility that not doing this will cause an unsolvable gridlock if there’s only space reliably for one more car.
The trouble is, that metric is not as simple as it sounds. For example some cars have aircon, some do not, some have radiators and exhausts, some do not. Should the metric be ‘tasks completed’ or ‘percentage progress towards export’?
As I imagined it, a car would have value for “where am I going next?” with the stations numbered in the order they appear in the build list, with the car with the higher number going first; on the assumption that they’d never need to go back to an earlier station and that a car that doesn’t need a thing would skip that station when deciding where to go.
PS. By no means am I saying how the game should be architected.