Alexander very well knew the design for his roads was a bit of an overkill.
He could easily get away with decreasing by at least a third if not half.
But since he was building the damn thing, he thought he might as well finish in one go.
He knew very well just how hard it was to restart such a huge project once it was done.
Any further modification, even an inch of width increase would require hiring almost nearly the same amount of people and more than that, produce all sorts of discontent among the lords about them losing their land.
Because Alexander was not paying to 'use' their land.
So since his treasury was now full and he had the political capital to force the nobles to let him build roads through their territory without compensation, he was determined to see it through.
Thus he brushed off Uzak's idea of doing it half now and leaving the rest for later.