The Sydney Harbour Tunnel is a twin-tube road tunnel in Sydney, Australia. The tunnel was completed and opened to traffic in August 1992 to provide a vehicular crossing of Sydney Harbour to alleviate congestion on the Sydney Harbour Bridge. It is the tunnel under the harbour, although there are plans to build a set of rail tunnels. The tunnel joins the Warringah Freeway at North Sydney, and the Cahill Expressway at the entrance to the Domain Tunnel. It has two lanes in each direction, and runs at an angle of thirty degrees to the Sydney Harbour Bridge. In 2008, the tunnel was carrying around 90,000 vehicles per day, the tunnel is made up of three sections, twin 900-metre land tunnels on the north shore, twin 400-metre land tunnels on the south shore and a 960-metre immersed tube structure. The tunnel falls about 55 metres from the entrance and about 35 metres from the southern entrance to its deepest point,25 metres below sea level. The IMT structure consists of eight precast concrete units, the units were constructed over 100 kilometres away in a casting basin at Port Kembla and then towed to Sydney Harbour. A trench was dredged before the arrival of the IMTs and then the IMTs were lowered into the trench by a system of pontoons and control towers. After the IMTs were in place the trenches were backfilled and then a rock armour was placed over the top to protect the units against marine hazards, the land tunnels were constructed by a combination of driving and cut-and-cover techniques. The total construction cost of the project was A$554.25 million, the northern end pylons of the Sydney Harbour Bridge were altered to allow for air exhaust from the tunnel to rise over the harbour. Bradfield Park on the side of the bridge also has air intakes. Fresh air is drawn by an underground station on the north shore and is pumped to all sections of the tunnel through vented ducts. The air supply uses fourteen axial flow fans, each up to 2.5 metres in diameter, the exhaust uses sixteen fans that draw exhaust air through two underground ducts from the tunnel ventillation station and transfer the air to the top of the pylon. Each of the fans has a duty of 53 to 103 m³/s, the tunnel was opened to the public to walk through from North Sydney to South Sydney on 30 August 1992. The proceeds of the tickets sold for this event were donated to the Royal Institute for Deaf, the tunnel opened to traffic on 31 August 1992. The Harbour Tunnel is a partnership between the Government of New South Wales and private investors by tender, at the conclusion of the operating contract in August 2022, the tunnel is to be handed back to the NSW Government. In 2006, the New South Wales Government announced that all cash tolls on the Sydney Orbital Network will cease by 2010 and this measure has substantially eased the traffic jams heading towards the electronic gantries, and providing increased convenience and time savings
Sydney Harbour Tunnel, northbound
Alterations to the northern end pylons of the bridge were required in order to build the tunnel.
Southern entrance to the Sydney Harbour Tunnel, heading northbound