The North Had More Railroad and Used it Efficiently (this is a URL)
This source is a letter from Robert E. Lee to Jefferson Davis. In this letter Lee writes that "every train brings its recruits" in reference to the Union Army. This shows that the north used the railroad to their advantage in order to move troops across the country efficiently. Also, Lee states that "The Baltimore & Ohio Railroad is very closely guarded along its whole extent." This shows that the north understood the importance of the railroad and guarded it closely to keep its advantages.