Hong Kong MTR is one of the busiest in the world, it's also I believe the timeliest in the world (three 9's [1]) and serves 1.6 billion per year. These things definitely work. MTR does such a good job operating in HK that they were tapped to run the new Elizabeth line in London as MTR Crossrail.

[1] http://www.mtr.com.hk/en/customer/main/performance_201407.ht...