The Big Dig is the unofficial name of the Central Artery/Tunnel Project (CA/T), a massive undertaking to route the Central Artery (Interstate 93), the chief controlled-access highway through the heart of Boston, Massachusetts, into a tunnel under the city, replacing a previous elevated roadway. The project also included the construction of the Ted Williams Tunnel (extending Interstate 90 to Logan International Airport) and the Zakim Bunker Hill Bridge over the Charles River. At the time, the Big Dig was the most expensive single highway project in American history. When the last major highway section opened in December 2003, over $14.6 billion had been spent in federal and state tax dollars. http://en.wikipedia.org/wiki/Big_Dig