BIG DIG'S NEW GIG

Construction of four huge interchanges is a pivotal point for Boston's $10.8-billion Central Artery/Tunnel (CA/T), which has been under way since 1986 to replace a 50-year-old hulking viaduct that now slices through the city and is almost perpetually clogged. In its place will be an eight-lane highway partially underground, public space above, and new connections for the city's major arteries. Workers are building 170 lane mi (274 lane km) of roadway, half subterranean, in a congested 7.5-mi-long (12-km) area. Of all the interchanges being tackled, none has challenged the CA/T team as much as the South Bay Interchange. The structure, which will directly link east-west Interstate 90 with north-south Interstate 93, is being built on five separate levels around nine railroad tracks emanating from the nearby South Station.