As always the answer is some synthesis of the many viewpoints. Above-ground routes are much easier (thus cheaper) to adapt and change. Connecting outer-suburbs

As always the answer is some synthesis of the many viewpoints. Above-ground routes are much easier (thus cheaper) to adapt and change. Connecting outer-suburbs to an existing underground network is extremely difficult, it takes decades. It's hard to increase the capacity of existing networks. Not to say they aren't useful, but increasing capacity with above-ground cycle networks is much easier. Encouraging people to cycle for shorter journeys further frees up capacity for longer trips where trains make more sense. Roads as they are currently massively favour cars, to an unacceptable degree. I would cycle where I am if it didn't substantially increase my risk of death.