Bus Stops.
Short and sweet, bus stops. Record an "detour" from your main road route pulling to the side of the road, give it plenty of room distance wise so two or maybe even three semi-truck grain trailers can fit to this detour, then place target point after which you pull back to the main road network route waypoint line again.
For very large fields and large scale operations you could record this kind of grain trailer parking spot or bus stop whatever you want to call that detour, to all four sides of the field (assuming its somewhat square). Now you could have completely stress free failure safe semi-truck grain trailer operation going on and no tractor with grain cart auger wagon would have to sit and wait for empty semi's arriving to the field as there would always be enough.
Here is a snippet of one of my Start From Zero stories:
Then recorded autodrive network waypoint routes for F220 E, S, W and N grain loading points. Now semi-trucks can park indepentendly to any of these without causing traffic jams and preventing from already full semi's passing by. Pretty cool setup. I really like the new autodrive grain loading points I recorded for each side of the field so that they are kind of like a bus stops along the road, that other semi-trucks or any vehicles for that matter can drive through there without getting into a traffic jam. Besides if you are a super realism purist, its unrealistic to just stop and park your grain trailer in middle of a county road, its just not happening, by side of the road sure but not ON the road like all my other autodrive target points have been so far. I'm going to be using this method on all large fields, it might be a bit excessive for small fields to make them on all sides, but for large ones where grain cart is driving with a red face and sweat dripping all over the place, yes absolutely. Big boy target points.