The first phase of New York City's Second Avenue Subway (extending the Q line to 96th St) cost a staggering $4.5 billion for just 1.5 miles of track and three new stations. Opened in 2017, it is statistically the most expensive subway project per mile in human history. In 2026, Phase 2 is underway, with a budget that has ballooned further; it is expected to cost over $7.7 billion to extend the line into East Harlem. This high-value price tag is driven by the extreme complexity of tunneling through "high-density" Manhattan schist, moving ancient utility lines, and building deep-level stations that must meet modern ADA and safety standards. For a peer-to-peer perspective, while the cost is astronomical, the line provides a vital high-value "release valve" for the overcrowded Lexington Avenue lines. Critics often point to these costs as a warning of how difficult urban infrastructure has become, but for the 200,000 daily riders, the "stubway" has already transformed the commute of the Upper East Side.