you could maybe add more destination output fields (as many as one likes to use) and as many trucks as one likes to have. but scale the price for the transport much harder based on distance. so you would use trade routes for long distance because it is cheaper and not just because the other mechanic is so tricky to use.
if you want to force trade routes upon the player please remove the destination tab so everything is done with trade routes. it is just not fun to make the mechanic as cumbersome as possible just to enforce the use of trade routes. this is not a puzzler but a simulation so i think doing the whole transport stuff as a player should not be micro management of every truck. please rethink the concept.