if the difference between the weight of the truck and the load will be in the direction of the towing vehicle - the cargo some speed will be announced, which will depend on the weight of the towing vehicle to the value of the Enlarged trailer weight, and power of the tractor engine.
that is, if my “bus” weighs 10 tons and I need to pull a truck that weighs 6 tons - that my motor will have to carry 16 tons and it will go to, respectively, to change the maximum speed. Of course, provided that the “trailer” will be equipped with at least four wheels. ie, that the trailer is not turned into a scraper. but on wheels, so I think you can, and take care. it is still faster than a fully disassemble interfering passage of transport.
but if I trucks of 2 tons will try to drag a tank weighing 20 tons - that I have, of course, will not work, because the rest mass of the tractor with my very small.
I think the mathematical apparatus of the game is quite capable to perform this kind of calculation.
and problems with the animation “trains” of this kind - to spit on them for the first time.