The first note is how much more development there is now compared to when the lines were put in:
The subway forever altered the city it was designed to serve. In 1910 most of Brooklyn was undeveloped, and much of it was still farmland. But the BMT changed all that. By 1940 Brooklyn had more residents than Manhattan, and neighborhoods like Sheepshead Bay, Canarsie and Bay Ridge were no longer remote. Similarly, the Bronx counted only 200,000 residents in 1900. By 1940, the population was seven times that, and the Grand Concourse, Loews Paradise and Krum’s ice cream parlor were already legendary.
Transit causes development, no question.
Without the subway, it’s hard to imagine that New York would have remained a great city, indeed the ultimate city. Urban greatness, in the 21st century no less than the 20th, requires an efficient, safe and effective rail transit system. Without the subway, New York might very well have turned out to be Bridgeport.
What would Seattle be like if we had built a subway? I don’t know. But we are building rail transit now, and if we continue to build it we can see whether Seattle can achieve “urban greatness”.