You can't compare 'New Jersey' with the Netherlands (though, you could compared it to say the province of Utrecht) they are at different levels in the 'org' and that has massive effects for things like public transport. In order to get coast to coast public transport you'd have to take the whole of the country (the United States) into account and then you'll find that that average population density suddenly matters a lot.
Of course you can always chop up that big country into many small pieces and then focus on the few that are above the average of any other country but that's not a useful thing to do.