- "Porter Tunnel, a major project to link the city together, but it is promissed by City Hall that building will be complete some time in 2001."
- — GTA III Website.
The Porter Tunnel is the major road tunnel system in Liberty City, possibly based on the Holland Tunnel, Lincoln Tunnel or the Queens-Midtown Tunnel. It appears in Grand Theft Auto III and Grand Theft Auto: Liberty City Stories, but does not appear in Grand Theft Auto Advance, since the game is viewed from a top-down perspective.
The Porter Tunnel is primarily a dual carriageway (4 lanes, 2 each direction) underground and underwater road tunnel (the Staunton Island exit is a single carriageway and has only one lane for each direction), which connects all boroughs in Liberty City: Portland via Harwood, Staunton Island via Rockford, and Shoreside Vale via Francis International Airport and Wichita Gardens.
The tunnel is actually a system of three separate tunnels, two of which branch out from one long-running tunnel from Harwood to Wichita Gardens, while the branch tunnels lead to Rockford and Francis International. The Francis International portal consists of two separate openings on either side of a surface road, each for one traffic direction.
Much of the tunnel runs underwater.
GTA Liberty City Stories
In 1998 (the time setting of GTA Liberty City Stories), the tunnel is revealed to be only partially completed, as only the Shoreside Vale ends of the tunnel are operational, while the Shoreside Vale-Staunton stretch is still under construction; digging towards Portland had not even begun (an issue further suggesting the late completion date for October 2001). At the time, the tunnel's future Portland exit is occupied by the Portland ferry terminal, which is temporarily shut down following city-wide protests against the construction of both Callahan Bridge and the tunnel, which will render the ferries obsolete. The ferry returns to service after compromises and assurance by a newly elected mayor to retain the ferry service, but was ultimately shut down, its Portland terminal cleared away for the Porter exit.
In 2001 (the time setting of GTA III), the tunnel is initially inaccessible, citing that tunnel construction was still incomplete and had been delayed several times. At the time of the tunnel's delays, the tunnel's chief engineer and project director is Winston Cole, while the project's financier is FBC Finance Group. The tunnel was originally scheduled for completion in April 2001, but was delayed to late-October 2001, coinciding with GTA III's timeline. The projects has been plagued with problems, such as leakage, as well as corruption, leading to the project winding up over-budgeted and behind schedule.
During the game, the tunnel would be opened to the player in phases: first with the segment linking Portland and Staunton following "Last Requests", then the segment linking the Portland-Staunton exits to the Shoreside Vale exits following "A Drop In The Ocean".
If the player manages to reach Staunton before it is unlocked after "Last Requests", the tunnel is revealed to only be sealed from the Portland end, allowing the player to access Shoreside Vale via the tunnel (as the Shoreside Lift Bridge remains non-operational). After "Last Requests", the route to the Shoreside Vale exits is sealed off from traffic until "A Drop in the Ocean". If the player ventures towards into the Shoreside stretch, traffic between the two Shoreside Vale portals is revealed to be free flowing, lending to the idea in GTA Liberty City Stories that these ends of the tunnel have been opened to the public longer than the Staunton and Portland ends.
- The condition of the tunnel in GTA Liberty City Stories seems to contradict what is established in GTA III - while GTA III states the tunnel was constructed in stages from the Portland end, Liberty City Stories instead shows that the opposite is true, with the Shoreside Vale end being the first to be completed.
- In GTA III, before Staunton Island is unlocked, using a glitch, it is possible to get into the tunnel and go to either of the locked islands.
- If you try the Porter Tunnel glitch on Staunton Island, you don't have any choice to go out of the tunnel except dying. In GTA III, the Staunton Island exit is quite dangerous, because the roads are narrow.
- In GTA III, cars on the Shoreside Vale end of the tunnel, near the airport exit, may drive onto the side barriers. This is more than likely a glitch.
- GTA Liberty City Stories Porter Tunnel glitch, a video depicting an exploit allowing the player to access the unfinished portions of the tunnel.