I think if people were willing to make a little more effort, cart paths could be more easily hidden. They make 'dyes' for concrete. So it would be fairly easy to dye the concrete a green or brown color and blend it in with either grass, pine straw or any number of other things. (And for those who try to say I'm wrong, whatever, I've poured more concrete than I care to remember, I know it would not be terribly easy to dye 5 miles of concrete, but it wouldn't be terribly hard either) At least with some dye, it wouldn't be as intrusive as a plain gray path.