O'Neill Tunnel in the context of "Tip O'Neill"

The Big Dig was a megaproject in Boston that rerouted the elevated Central Artery of Interstate 93 into the O'Neill Tunnel and built the Ted Williams Tunnel to extend Interstate 90 to Logan International Airport. Those two projects were the origin of the official name, the Central Artery/Tunnel Project (CA/T Project). The megaproject constructed the Zakim Bunker Hill Bridge over the Charles River, created the Rose Kennedy Greenway in the space vacated by the previous elevated roadway and funded more than a dozen projects to improve the region's public transportation system. Planning began in 1982 and construction was carried out between 1991 and 2006. The project concluded in December 2007.

The project's general contractor was Bechtel, with Parsons Brinckerhoff as the engineers, who worked as a consortium, both overseen by the Massachusetts Highway Department. The Big Dig was the most expensive highway project in the United States, and was plagued by cost overruns, delays, leaks, design flaws, accusations of poor execution and use of substandard materials, criminal charges and arrests, and the death of one motorist.

The Central Artery (officially the John F. Fitzgerald Expressway) is the concurrent section of Interstate 93, US 1 and Route 3 through Downtown Boston, Massachusetts, United States. The modern-day Artery, built as part of the Big Dig from 1995 until 2003, begins at the Southeast Expressway in the South End. Traveling north, it has an interchange with the east–west Massachusetts Turnpike (I-90), and travels beneath the Financial District and Government Center through the O'Neill Tunnel. Route 3 exits onto the Leverett Connector within the tunnel in Charlestown; US 1 exits aboveground from the Zakim Bridge onto the Tobin Bridge, and I-93 continues on the Northern Expressway toward New Hampshire beyond the bridge.

The original Artery, constructed in the 1950s, was named after John F. Fitzgerald; it was partly elevated and partly tunneled. Its reputation for congestion inspired the local nicknames "The Distressway," "the largest parking lot in the world", and "the other Green Monster" (the paint of the highway girders shared the same color as the left field wall at Fenway Park). The original Artery was demolished after the O'Neill Tunnel was completed, and was replaced with the Rose Fitzgerald Kennedy Greenway, named after the daughter of John F. Fitzgerald and the mother of John F. Kennedy.