It runs from the Zakim Bunker Hill Bridge at its north portal—barely 165 feet (50 m) east of the TD Garden sports facility's eastern corner—to Boston's Chinatown at its south portal.

The tunnel is named for Tip O'Neill, former Speaker of the United States House of Representatives, whose constituency included several of the surrounding communities in Metro Boston.

This was followed in 1996 by the beginning of construction on the tunnels with the pouring of slurry to build walls,[2] which was preceded by underpinning the expressway.

The state legislature and the Massachusetts delegation to Congress opposed the choice, and it was officially named after O'Neill (a longtime Speaker of the United States House of Representatives) by Section 1930 of the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU), which was passed by Congress and signed by then-President George W. Bush in 2005.

Due to the location of the tunnel near the ocean, brackish water was able to seep into cracks within the concrete, which have had the potential to cause flooding.