I was wondering if it might be which way the road is layed down, as in From - To. That can be tested I guess.
As you noted vieuxchat, it is probably just a random loading of the caravan, so it reports something when moused over,without any worries, yet, about what is going where.
The current model prevents any large scale hauling so I guess the Loss of resources would be so limited, 3 food, 4 timber (supposing a 1-1 scale) we have to wait to see the true impact that could be wrought.