Is it a function of population density to make this economically feasible? Some US states could meet the criterion, but financing is difficult because rights-o

Is it a function of population density to make this economically feasible? Some US states could meet the criterion, but financing is difficult because rights-of-way are so expensive. Europe: 87 people per sq mile Germany: 623 ppsm Italy: 532 ppsm UK: 727 ppsm United States 93 District of Columbia 10,984 New Jersey 1,260 Rhode Island 1,059 Massachusetts 895 Connecticut 744 Maryland 635 Delaware 514 New York 420 Florida 406 Pennsylvania 289 Ohio 288 California 251