Dozens of people have been injured in a head-on collision between two commuter trains in the Austrian capital Vienna.

BBC: Austrian trains in head-on crash

More than two million passengers travel daily on South Africa's commuter trains.

BBC: South Africa driver fired over Soweto train crash

Two decades of explosive growth based on roads, not commuter trains, have resulted in a population so widely dispersed that knitting it together again may prove almost impossible.

ECONOMIST: Cities and growth