Big Dig, Underground highway tunnel system in downtown Boston, United States
The Big Dig is an underground highway tunnel network beneath the streets of Boston, connecting Interstate 93 and Interstate 90. The subterranean lanes run for several kilometers and carry traffic through the city center.
Construction began in the early 1990s to replace the old elevated highway with underground tunnels. The project took over 15 years to complete and changed how traffic moves through Boston.
The removal of the elevated highway opened space for parks and public areas along the Rose Kennedy Greenway downtown. The new green spaces now connect neighborhoods that had been divided by the old roadway for decades.
The tunnels remain open around the clock for traffic and form a key north-south route through the city. Drivers should watch for signage, as several exits lead directly into the downtown area.
Engineers used ground freezing techniques to stabilize soil around existing subway tunnels during excavation. This method prevented settling and protected buildings standing above the construction zone downtown.
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