Wikipedia has a good summary of the construction techniques. Only 10% of it is just below street level using cut-and-cover technique. https://en.wikipedia.org/

Wikipedia has a good summary of the construction techniques. Only 10% of it is just below street level using cut-and-cover technique. https://en.wikipedia.org/wiki/Second_Avenue_Subway#Construction_methods https://en.wikipedia.org/wiki/Second_Avenue_Subway#Construct...