The Big Dig, officially known as the Central Artery/Tunnel Project, significantly reshaped Boston's transportation and urban landscape. Completed in 2006, this massive undertaking replaced a six-lane elevated highway with an underground expressway, easing traffic congestion in the city's downtown area.

The project's completion led to the creation of the Rose Fitzgerald Kennedy Greenway, a 17-acre public space, and improved air quality due to reduced carbon monoxide emissions. While it decreased commute times within the city, traffic worsened in the surrounding areas, and the project faced criticism for its flawed execution and escalating costs, reaching $24 billion with interest. Despite the controversies, the Big Dig provided greater access to Boston's Seaport District, spurring development with new hotels, restaurants, and cultural centers.

The Central Artery/Tunnel Project, known as the Big Dig, was needed because Boston's elevated Central Artery highway, built in 1959, could no longer handle the increasing traffic, choking the city and isolating neighborhoods. The project, started in 1991, replaced the elevated highway with an underground expressway, aiming to improve traffic flow without disrupting daily life. Despite issues during construction, the Big Dig reduced traffic congestion in downtown Boston and created new public spaces.

During the Big Dig project, workers faced significant challenges, including construction delays and massive cost overruns. The project was plagued with issues throughout its planning and construction. There were also instances of substandard materials, such as poor-quality concrete, which led to fraud arrests of six men who worked for the Big Dig’s largest concrete supplier. In 2004, thousands of leaks were discovered in the ceilings and walls of the new tunnels, and harbor saltwater corroded steel supports, one of which fell in 2011.