ˌBig ˈDig, the BrE AmE informal
a name given to the process of building the Central Artery/Tunnel (CA/T), a major new road system built under the city of Boston in the US. It goes under the city and connects several major roads with Logan Airport, Boston Harbor, and the city centre. The new road took many years to build, during which time it caused a lot of traffic problems in the city.