State Police Tunnels opened in December 1995, is located above the South Boston portal of the Ted Williams Tunnel (TWT). The TWT was originally designated as the Third Harbor Tunnel and was the first portion of the Central Artery/Tunnel Project (the 'Big Dig') to be completed, inaugurated on December 15, 1995. The Tunnels barracks covers 45 miles of highways, including all Big Dig roadways and the intricate system of highways, tunnels, ramps and connectors.
The Big Dig is the largest public works project in the nation's history and was constructed while maintaining service to the old elevated highways. Major roadways include: I-93 North from Exit 18 in South Bay to Exit 28 in Charlestown; I-93 South from Exit 26 in Somerville to the South Bay Mall in Dorchester; I-90 (MassPike) East and West between Interchange 19/20 in Allston Brighton and Route 1A in East Boston; the Leverett Connector North and South, between Somerville and Leverett Circle. Other tunnels covered by H-9 personnel are the Sumner and Callahan Tunnels under Boston Harbor, the CANA Tunnels under City Square in Charlestown, the Prudential and O'Neil Tunnels running east and west, and the most recent Liberty Tunnel running north and south along Route 93.