Most Influential Projects 2021

13 Mumbai Metro Line 3

Inside the Mumbai Metro tunnel

For digging deep to make transportation safer in one of the world’s most populous cities

Mumbai’s railway system typically serves more than 7 million commuters every day, but the jam-packed trains in the world’s eighth-largest city create risks that regularly injure and even kill riders. Although the rate of accidents declined with the drop in ridership in 2020 due to the pandemic, there were 2,691 deaths and 3,194 injuries reported in 2019. Looking to provide safe mass transit to its rapidly growing population, Mumbai Metro Rail Corp. (MMRC)—a consortium of India’s state and central governments—is building the city’s first underground train system. 

To deliver Mumbai Metro Line 3, the team first had to complete one of the world’s longest metro-tunneling projects, spanning 33.5 kilometers (20.8 miles) with 27 stations. Collaborating with design and engineering consultants including AECOM, Padeco, LBG and Egis Group, the team broke down the megaproject into two sections: The first is on pace to be delivered by December 2021, with the remaining section expected to be operational by mid-2022. 

“Tunneling in Mumbai is extremely challenging as the alignment passes through densely populated and congested parts of the city,” said Subodh Gupta, projects director, MMRC. “In addition, there are high-rise, heritage and dilapidated buildings, flyovers, metro viaducts and railway lines in close proximity.” 

To get the massive 360-foot (109.7-meter) tunnel-boring machines through Mumbai’s narrow streets, the team shipped them in parts, then reassembled them underground. During digging, a 36-foot-wide storm drain had to be dismantled and re-routed to make room for the tunnel. For another section, the team had to dive deeper, installing two 1.5-kilometer (0.9-mile-long) long tunnels underneath the Mithi River.

With 8,000 workers and 17 boring machines working 24 hours a day to stay on schedule, proactive planning helped the team mitigate possible disruptions. When the coronavirus threatened to grind work to a halt, project leaders created new safety protocols for workers in confined underground spaces: When one worker tested positive, the entire team was quarantined, forcing tunnel work to pause on several occasions. 

Aware that Mumbai’s monsoon season could dramatically slow progress, the team set up hundreds of worksite pumps to control flooding, and managers provided real-time updates to MMRC leadership via WhatsApp. The result? In the rare instance when rain halted work, it was only for a few hours.

With an estimated 1.6 million people expected to ride the subway daily, the team’s primary focus was building in safety and convenience. Upgrades include larger air-conditioned train cars, platform screens to prevent accidental falls or suicides, and escalators and elevators across stations. To protect historic buildings, project partner Sonneville also installed low-vibration track technology.

“MMRC specially considered the needs for the people in the city,” Sonneville President Peter Laborenz says. “This should lead to a new type of living, of having a better future.” 

The project also has an eye on reducing the city’s carbon footprint—and not just by getting vehicles off the road. In coordination with Forest Development Corp. of Maharashtra, MMRC is planting 9,000 trees and 8,888 mangroves to compensate for about 108 mangroves cut down during the construction of two train stations. 

Once the train is up and running, MMRC hopes Mumbai will not only get a much-improved transit system, but increased business investments and continued job creation.