john, I believe you have misunderstand the article. Figure 3 indicates you have an extremely steep drop in cupital costs per rider. With the inflection point at around 20 jobs or people people per acre. (Note jobs). The inflection point is the same for light rail. And the capital costs are not much different. Stations constructed at points where that occurs will insure ridership.  Simple examples would be the airport, ala moana, and pearl city and west oahu, which have jobs higher than that rate. The line is designed to go through a population dense corrider that meets these requirements. Beyond that you keep insisting that 600,000 is wrong, and that count is within 20 miles of the rail corrider. With buses feeding rail within that area. i'm  to the number being wrong, but provide a source. Census tracts from the 2010 census indicate otherwise. Here is a map with densities, note the line basically follows the high density corrider. 
http://www.ohadatabook.com/2010_pop_density.pdf