[fennecfoxen]

The London Underground does have a few advantages over New York, though -- they were able to build deep tube lines with ease because of the geology (the rock under Manhattan being much tougher to tunnel through). New York subways are almost entirely cut-and-cover, which places substantial constraints on where they run (under city streets, where you have to worry about nearby basements, and water mains and the like) and how much space there is to connect them to each other. This is also a reason they have more sharp curves that make terrible metal-on-metal squeaking sounds.

London's tube stations have a lot of space between their platforms, enough to provide a network of hallways with separate entrance and exit passageways and escalators (some of them are equipped with switchable wayfinding signs so you can have different ways out at morning and evening rush hour). New York doesn't have anything like that anywhere; you'll often have a single set of stairs from the street down to one side of the tracks (with no provision for transferring to the other side at all, to say nothing of elevators). If it's a nice, modern station the tracks will be a little deeper so the station entrance serves as an overpass over the tracks, but other times the transfers will only be available by walking along another subway platform.