The Callahan Tunnel is a vital transportation route located in Boston, Massachusetts. It connects the Central Artery to the Ted Williams Tunnel, facilitating traffic flow in and out of the city. Opened in 1995, the tunnel is part of the larger Big Dig project, which aimed to improve urban infrastructure and reduce congestion. Spanning approximately 1.6 miles, the Callahan Tunnel features two lanes in each direction. It is designed to accommodate both vehicles and emergency services, ensuring efficient travel for commuters. The tunnel plays a crucial role in the overall connectivity of the Boston metropolitan area.