It carries motor vehicles from the North End to Logan International Airport and Route 1A in East Boston.

It was named for the son of Turnpike chairman William F. Callahan, who was killed in Italy days before the end of World War II.

Under the relevant Turnpike regulations, a yellow signal light means "proceed only as directed", on penalty of a $50 fine.

[citation needed] Other markings in the tunnel include a "double white line" in the center, intended to discourage drivers from changing lanes, to be penalized with a $100 fine.

[3] During closures, Logan-bound traffic was diverted into the Ted Williams Tunnel, Tobin Bridge, and Massachusetts Route 1A South via Revere or East Boston.