Rail is particularly effective for navigation of a linear space where large numbers of people cover arbitrary segments of the distance. On a larger scale, think

Rail is particularly effective for navigation of a linear space where large numbers of people cover arbitrary segments of the distance. On a larger scale, think Italy, Japan, or the US East Coast. On a smaller scale, think avenues in NYC. Once navigation is extended to a two-dimensional area, Rail requires serious compromises. To the extent that you are going for arbitrary point-to-point travel in two-dimensional space, whether the vehicles are traveling on rails or tarmac is irrelevant -- the problems are largely the same, and it is easier to lay tarmac.