Something I have been thinking about:
NIMBYism, property values, and urban realm be damned, how much faster and cheaper would building the DRL above ground be? Underground transit in the developed world seems to be a dying trend. Besides Toronto, most rapid transit projects in North America and Europe are being built at or above grade, rather than below. The capital costs are simply becoming too high to push ahead with long underground tunnels, even if ridership fares are high enough to cover the maintenance and operating costs. New York is spending $6.5 billion for less than 4km of new subway, meanwhile Honolulu is building a whole new 32km elevated line for $5.3 billion, more than a billion less than NYC!