BTS Skytrain

In the 1990s Bangkok's traffic was globally infamous: commutes ran three hours, and drivers famously kept bottles — and sometimes portable toilets — in their cars. The Skytrain's 1999 opening was the day the city got 40 minutes of its life back per trip.

Thais call it 'rot fai fa' — literally 'sky train'. The entire original system was built elevated because the streets below were already unfixable: Bangkok simply added a second storey to itself.