[ashtonkem]

> Have any metro areas built entirely new subways where there were none before in recent times?

None that I can think of in the US, but Madrid is generally pointed to as the stellar example of rapid and cheap subway expansion. They added an unbelievable amount of track and stations at really low cost.

> Between 1995 and 2007, the Spanish capital swiftly and cost-effectively upgraded its subway system, building more than 150 new stations over 120 miles at costs far below New York City rates. First, in just four years, Madrid designed, constructed, and opened 39 new metro stations and laid 35 miles of rail, 23.5 miles of which required new tunneling. The expansion was unprecedented for its low costs (about $65 million per mile of rail) and speed. Then, between 2000 and 2003, Madrid built Metro Sur, a 28-station, 25-mile circular subway line that connects the densely populated municipalities south of the city. Simultaneously, Madrid completed a direct metro line from the city’s central business district to its airport, now a 12-minute train ride away. Finally, between 2004 and 2007, commuters in the Madrid region gained an additional 80 new metro and light-rail stations, at a cost of $6 billion.

Just like high speed rail, this was less of a revolution in public works, and more a series of unglamorous minor improvements that added up to something greater than the sum of its parts. The government aimed for speed above all else, with the understanding that delays and financial uncertainty are the doom of any large project. So they would hire multiple teams to bore tunnels at once, and pit them in friendly competitions to bore faster. They negotiated with local land and business owners over more interruptions over a shorter period of time to reduce lawsuits (a big issue in NYC subway expansion), and they designed all the stations to be modular so that they wouldn't waste a ton of time designing and constructing bespoke stations. The sum is that they got it done really fast and really cheap.

Ironically, it looks a bit like the way that we construct our highways.