You're mistaken. Decades before the New York Subway (opened 1904), you had the Cobble Hill Tunnel running three quarters of a kilometer under the streets of B

You're mistaken. Decades before the New York Subway (opened 1904), you had the Cobble Hill Tunnel running three quarters of a kilometer under the streets of Brooklyn (1844). And the New York Subway was preceded in an much more substantial way by the Metropolitan Railway in London (proposed in the 1830s, began construction in the 1850s), that would eventually become the London Underground. The Metropolitian Railway took a conservative incremental approach to existing technology. The locomotives were steam and the tunnels were cut and cover. Subway systems as we know them to day are the product of nearly two centuries of incrementing on already proven technology. If you want a real example of a 19th century Gadgetbahn in New York, the obvious example is the Beach Pneumatic Transit (which was a total flop and was remarkably similar to Elon's "hyperloop" in numerous other ways as well.)