> "And since typical human nature is to not think of the "what can go wrong" scenarios before they actually go wrong, those same planners likely never considere

> "And since typical human nature is to not think of the "what can go wrong" scenarios before they actually go wrong, those same planners likely never considered the "how do we fix track in tunnel 2 without having to half shut the system down to do so?" aspects of their decisions at the time." Having met transit planners before, I think you're probably not giving them enough credit. The sort of hellish clusterfuck that happens when things go wrong in a 2-track system is well understood and not new even during Metro's planning and construction. More likely it was decided that a 2-track system that went straight to hell the moment something went wrong is a better choice than nothing at all, which is the alternative. It's not that they were trying to save money, but rather trying to fit the system within a budget that simply couldn't get any larger. Same deal here in NYC - the new Second Avenue Subway is 2-track even though everyone, the MTA included, knows the problems inherent in it. The problem is that there is literally no way to cough up enough money to make it a 3- or 4-track subway. Public transit has been a dirty word in American politics for over half a century, and the willingness to invest isn't much different. These weren't short-sighted decisions, they were entirely cognizant of the shortcomings, but there wasn't any other choice.