Get all the dirt you need for the road. Then get say, another 64 dirt. Face the ground, jump and place a piece of dirt underneath you. Do this as high as you want to dirt road to be. Hold shift (this makes it so you cannot fall off the tower) and go to the very edge of the dirt block. There will be just enough of the side so that you can place a block. Repeat untill you have built your road.
~miklvy