Not necessarily. More, smaller trucks will mean your transport costs will go up because you get less economy of scale. Eliminating the driver helps mitigate that of course, but going to smaller trucks then eliminates the savings you got by eliminating the driver. Having more, smaller trucks would be more versatile however, if you don't need to transport full truckloads of cargo between certain points.

Also, drivers as I understand it aren't paid monthly salaries, they're paid by the mile.