A 6.5-kilometre tunnel which will create a third crossing across Sydney Harbour is set to start after receiving the green light for construction.

In a joint statement issued last week, NSW Minister for Transport and Roads Andrew Constance and Minister for Planning and Public Spaces Rob Stokes announced that Western Harbour Tunnel and Warringah Freeway Upgrade project has received planning approval subject to conditions.

Set to reduce pressure on existing Sydney Harbour road crossings (see below), the project involves construction of new twin 6.5-kilometre tunnels underneath Sydney Harbour as well as upgrades to the Warringah Freeway to integrate the new motorway with the existing road network.

The new tunnels will have three lanes in each direction and will connect the M4-M5 Link at Rozelle on the southern side of the Harbour to the Warringah Freeway near Cammeray on the northern side.

For most of their length, the tunnels will be mainline tunnels and will be constructed using road headers.

This is the most comment road tunnel construction method in Sydney courtesy of the high-quality sandstone beneath most of the city along with the wide cross section  which is needed for road tunnels.

For the section which crosses underneath the water between Birchgrove and Balls Head, however, an immersed tube tunnel similar to the existing Sydney Harbour tunnel will be used.

This section of the tunnel will be constructed by dredging a trench across the bed of the Harbour between Birchgrove and Waverton and installing prefabricated tunnel units to form the Harbour crossing.

Such a method will reduce risks associated with deep tunnelling in an area of poor geology under the Harbour.

It will also deliver the lowest possible gradient for connections to the Warringah Freeway in light of the large elevation change to North Sydney.

The project will complement the Beaches Link and Gore Hill Freeway Connection project (currently undergoing environmental assessment), which will deliver a new motorway tunnel connection across Middle Harbour from the Warringah Freeway and Gore Hill Freeway to the Burnt Bridge Creek Deviation at Balgowlah and Wakehurst Parkway at Killarney Heights

According to the project’s environmental impact statement, the new Harbour tunnel is necessary to help relieve pressure upon existing Harbour crossings at the Sydney Harbour Bridge and Sydney Harbour Tunnel, which cater for 165,000 vehicles and 94,000 vehicles respectively each day.

According to an Infrastructure Australia analysis in 2016, congestion costs on the corridor involving the Sydney Harbour Bridge, the Eastern Distributor, the Warringah Freeway and the Gore Hill Freeway amounted to $65,000 each day.

By 2037, demand for this corridor is expected to increase by 17 percent.

Conditions of the project’s approval include an investigation of more footpaths and cycleways in the area along with a requirement that any trees removed by replaced at a ratio of two-to-one.

A survey of local residents and businesses will be carried out in early 2021 to ensure that the project team understands and can mitigate the impact of construction.

Construction is expected to start in the first quarter of this year following the procurement process and the awarding of projects.

The first stage of the project involves an upgrade to four kilometres on the Warringah Freeway.

In a statement, Minister for Transport and Roads Andrew Constance said the project will slash travel times from North Sydney to Sydney Olympic Park by up to 20 minutes.

“The Western Harbour Tunnel will take pressure off the Sydney Harbour Bridge, Sydney Harbour Tunnel, Anzac Bridge and Western Distributor corridors to revolutionise transport capacity in and around our city,” Constance said.

The new tunnel will start at the new Rozelle Interchange and head under the Harbour to the Warringah Freeway, and will integrate new and existing public transport connections.

“This city-shaping piece of infrastructure will deliver a vital boost to the NSW economy, with the tunnel and freeway upgrade, along with Beaches Link, expected to support around 15,000 full time equivalent jobs.”

Minister for Planning and Public Spaces Rob Stokes said the project will transform the way people move across our harbour, with traffic volumes to be reduced on some of Sydney’s busiest roads.

(top image by tksteven via Wikipedia)