As I understand it, the north had a lot more distance of rail laid at the start of the war and continued to expand that throughout the war whereas the south not only started with less, but also had their rails damaged regularly without the industrial abilities to repair them.
How much did this matter to the actual outcome of the war? Were rails a very important part of Civil War logistics, or were moving things by boat or through regular land methods more common?
They were very nice for initial mobilization and deploying extra troops, but since almost all of the war was fought in the south, they didn't provide as much of an advantage as they could have. Also, a majority of the rail lines ran east to west rather than north to south, resulting in transportation patterns that could be clunky and restrictive at times given that the war was fought north to south. Overall they certainly helped the north to some degree, but their impact looks bigger on paper than it actually ended up being. Transport by boat, and especially cutting off the South's water based trade had a bigger impact on the outcome of the war than differences in rail infrastructure did.