London's Jubilee and Elizabeth lines were extremely complex and threaded through other subway lines and infrastructure. They too were on the drawing board for

London's Jubilee and Elizabeth lines were extremely complex and threaded through other subway lines and infrastructure. They too were on the drawing board for decades, and in the case of the Jubilee line, did not start until a new boring technique called the bentonite shield was invented. London should be in the same ballpark as New York but the article suggests it is 3-5x cheaper per mile.