My understanding is that building subways in LA is costlier and more labor-intensive than in a lot of the cities you mentioned, but the subway system is current

My understanding is that building subways in LA is costlier and more labor-intensive than in a lot of the cities you mentioned, but the subway system is currently undergoing a massive expansion in LA. The main difficulties are the fault lines: Subway lines have to be meticulously planned to avoid the dozens of faults as well as other areas that are susceptible to major movement. http://www.cccarto.com/faults/la_faults/ http://www.cccarto.com/faults/la_faults/