Operations at a Mumbai Metro Rail Corp. Tunnel Excavation Site

A worker climbs a flight of steps at an excavation site, managed by Larsen & Toubro and Shanghai Tunnel Engineering Co. (L&T-STEC), of a launching shaft for Metro Line 3, operated by the Mumbai Metro Rail Corporation in the Marol area of Mumbai, India, on Friday, June 16, 2017. The expanding mega city's suburban railway is one of the most crowded and among the most dangerous in the world. That's why there's an 800 billion rupee ($12.5 billion) project under way to build a new, rapid transit system that will carry an estimated 7 million more passengers making it busier than Metros in New York and London. Photographer: Dhiraj Singh/Bloomberg via Getty Images