ORIGINAL: golden delicious
Trucks move 5 times faster- provided you have a good road and no traffic jams. You'll also find they load and unload at the same speed. Perhaps twice the deliveries.
Poor roads would impact horse carts just as much as trucks. Four times as many vehicles for the same lift means much worse traffic jams for horse carts. Loading and unloading can take place at night - when, as you mentioned, transport would most likely not take place. Regardless, if the front lines are hundreds of miles from the supply head, the supply columns are well spread out, and there are few traffic jams. Five times faster and four times the lift still equals 20 times the delivery - truck vs horse cart.
So we have 2x2 = 4x. That's presuming the trucks remain in good condition all the time, and that fuel is available (harder to forage for than horse fodder)
Horses drop dead - and can't be repaired once they do. Alternately, they can become fatigued. Time for foraging cuts the duty-cycle for horse teams accordingly.
