Vietnam is one of Asia’s fastest-growing countries, and its two main metropolises in Hanoi and Ho Chi Minh City are the engine rooms of the economy. The city has 21·6 km of operational metro lines now, and another 55·1 km are under construction. Many more metro lines are planned, but these are all in the early planning phase without finalised alignments or official completion dates. Ho Chi Minh City ambitionsLike its northern counterpart, Ho Chi Minh City has made ambitious announcements about its future urban rail network. Intended eventually to form a loop line, Line 6 will initially run in a northern semicircle to link Tan Son Nhat Airport to Phu Huu.