Building a new subway line in New York City is an infamously slow and multi-decade process due to the city's dense underground infrastructure, complex legal environment, and astronomical costs. For example, the Second Avenue Subway was originally proposed in the 1920s, but "Phase 1" (which added just three new stations) did not open until January 2017—nearly a century after its conception. The actual physical construction of that first phase took roughly 10 years, beginning in 2007. The current Phase 2, which aims to extend the line to 125th Street, is expected to take another 7 to 9 years of active construction once fully underway. Factors such as the need for massive tunnel boring machines (TBMs), the relocation of centuries-old utility pipes, and the requirement to minimize surface disruption in some of the world's most expensive real estate make NYC subway projects some of the most expensive and time-intensive engineering feats on the planet. Generally, from the first "shovel in the ground" to the first train run, a single new station or short extension typically takes a minimum of 8 to 12 years.