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What is the Big Dig?

The Big Dig was an ambitious urban engineering project in Boston, transforming its landscape by rerouting the central artery of Interstate 93 into tunnels. It's a tale of innovation, challenges, and the reshaping of a city's heart. How did this colossal undertaking impact Boston, and what lessons does it hold for future infrastructure projects? Join us to uncover the story.
O. Wallace
O. Wallace

The Big Dig is officially known as the Central Artery/Tunnel Project (CA/T). It is the Massachusetts Turnpike Authority’s (MTA) big solution to what has become an equally big problem in the city of Boston: traffic, and lots of it. In 1959 when Boston’s elevated Central Artery, or I-93 opened, it was sufficient to carry the 75,000 vehicles that traveled its six lanes every day.

However, city planners had failed to recognize that the future would be much more congested — by the end of the 20th century, more than 200,000 vehicles would be traveling the same stretch of road. Poor highway design and increasing traffic made Boston one of the most congested cities to live in, with an accident rate nearly four times the national rate for a city. Some forecasted that by 2010, if no action was taken, Boston would have a veritable 16 hour “rush hour.”

Man with a drill
Man with a drill

The Central Artery was doomed to fail even as it was being built. It displaced approximately 20,000 residents, was difficult to drive, had inconvenient on ramps and off ramps, and cut off at least two Boston neighborhoods — the North End and Waterfront. Within a few years of its opening, plans were already underway for the Big Dig. In 1982, planning began, and in 1990, Congress approved 755 million US Dollars (USD) to contribute to the project. Construction on the Big Dig began in 1991. Its plan: to build a subterranean expressway below the existing elevated Central Artery, as well as tunnels running under the harbor, new bridges and interchanges.

The highway would have 8 to 10 lanes and end on the north side with a 14 lane, two bridge span of the Charles River. The first phase, the Ted Williams Tunnel, was completed in 1995, and runs under the harbor. In 1999, the Broadway Bridge and the Leverett Circle Connector Bridge was opened to the public. The Leonard P. Zakim Bunker Hill Bridge, completed in 2002, breaks records by being the widest ever built, and the first that employs an asymmetrical plan. By 2004, the elevated span of the Central Artery was torn down, and by May of 2007, the Big Dig was reportedly 99% complete.

The Big Dig, which has been compared to other massive undertakings such as the Panama Canal, has included 7.8 miles (12.5 km) of highway, which adds up to 161 lane miles (259 km), 50% of which is underground. The MTA has laid more than 3.8 million cubic yards of concrete that is 12 inches (30.48 cm) thick. More than 16 million cubic yards of soil has been removed, and is being put to use capping area landfills.

Today, carbon monoxide levels have been reduced by 12% in the city and 260 acres of land has been cleared, making way for 45 city parks. The Rose Kennedy Greenway is one of the largest, taking the place of a large portion of the elevated freeway. Part of the Big Dig has also included restoration of Boston’s shoreline, new sea walls and docks. Nearly 5,000 workers have been employed on the Big Dig, as well as numerous businesses and contractors.

At a cost of 14.6 billion USD, the Big Dig is one of the most expensive public projects. While many agree that it has been a great benefit to the city, there have been many associated obstacles and headaches. Shoddy materials and labor have been a major problem, as well as traffic and inconveniences created by ongoing construction. Despite any controversy, the Big Dig has made big changes benefiting the city as a whole.

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