"In 10 years" is a bit misleading, because that's just the construction time. You need to also take into account the time it took to go from "this would be a good idea" to actually starting to dig, because that's where the SF situation is currently bogged down.
http://www.crossrail.co.uk/route/crossrail-from-its-early-be... says the idea was first seriously proposed in 1974, and was then raised, dropped and batted around at various levels of politics for another 25 years before getting to "serious funded detailed feasibility study" in 2002, which didn't get the final go-ahead until 2008 (with the construction phase then being the 10 years after that and ending 2018).
http://www.crossrail.co.uk/route/crossrail-from-its-early-be... says the idea was first seriously proposed in 1974, and was then raised, dropped and batted around at various levels of politics for another 25 years before getting to "serious funded detailed feasibility study" in 2002, which didn't get the final go-ahead until 2008 (with the construction phase then being the 10 years after that and ending 2018).