Most of WestConnex will be in underground motorway tunnels, to minimise the need for land acquisition and remove through traffic from local streets.

Key features

WestConnex tunnels will be taller, wider and less steep than older Sydney tunnels, resulting in a smoother ride for motorists. Tunnels have efficient and modern ventilation systems that meet stringent air quality standards. See more about air quality and ventilation.

Each of the underground tunnels have a different number of lanes: 

  • M4 East - three lanes in each direction between Homebush and Haberfield 
  • New M5 - mainly marked for two lanes in each direction between Kingsgrove and St Peters. Wide enough to accomodate three lanes in future if needed
  • M4-M5 Link tunnels - up to four lanes in each direction.

Tunnelling is now complete on the New M4, with the average tunnel depth of around 35 metres and a maximum depth of 50 metres.

Tunnel routes

Our special online tunnelling maps assist people wanting to explore the depth and location of:

Building underground tunnels 

WestConnex tunnels are being built in good-quality Hawkesbury sandstone and Ashfield shale. The M4 East tunnels will be built with roadheaders and traditional rock-breaking methods, while the New M5 tunnels will be built using roadheaders and a technique called blasting.  Blasting is only used in locations where the geology is suitable.

Roadheader machines will excavate sandstone from the upper two-thirds of the tunnel to create the tunnel crown, while rock-breakers or blasting will be used to excavate the lower third of the tunnels.

What to expect during tunnelling 

The depth of the WestConnex tunnels means any impact on the properties above is highly unlikely.

To give further peace of mind to local residents and businesses, all properties within a zone on the surface equal to 50 metres from the outer edge of the underground tunnels will be offered a property condition survey both before and after construction. This will ensure there is a clear record of the property’s condition. Any damage attributed to the project will be repaired at no cost to the property owner. 

For all our projects, we notify residents when we are sure they will be within 50 metres of the underground tunnel, and explain the position and depth of the underground tunnel in relation to their property.

Once the new tunnel is operational, residents above the underground tunnels are unlikely to be able to hear or feel any vibration from the motorway.