Air quality

Air quality in Sydney has improved over time through more fuel-efficient vehicles and improved infrastructure design. 

WestConnex underground motorway tunnels are wider, flatter and higher than most other tunnels in Sydney, meaning a smoother journey with less stop-start driving and fewer vehicle emissions – including greenhouse gases.

In fact, by 2021, WestConnex will reduce carbon dioxide (CO2) emissions by more than 610,000 tonnes. By 2031 this rises to 1,417,420 tonnes.

Air quality assessments included in the M4 East and New M5 Environmental Impact Statements show that regional air quality is unlikely to change as a result of WestConnex. In fact, WestConnex will result in improvements in some areas where traffic uses the underground motorway tunnels instead of surface roads. 

Air Quality Consultative Committees

In 2017, Sydney Motorway Corporation (SMC) established the Air Quality Community Consultative Committee (AQCCC) for the M4 East (Stage 1) project and the New M5 (Stage 2) project. 

Tunnel ventilation

WestConnex ventilation facilities are in line with the world’s best practice to meet strict guidelines on air quality. They are safe for motorists and the community.

WestConnex tunnels use longitudinal ventilation systems, which require vehicles to draw in fresh air. The air from the tunnel is then released through ventilation facilities, supported by fans, which control air movement within the tunnel. The ventilation system is automatically controlled using real-time traffic data – taking into account traffic mix and speed, plus feedback from air quality sensors in the tunnel. 

Usually each tunnel has a ventilation facility at the beginning and end, with up to three for each section. The exact number is confirmed during design. See our interactive map for details. 

Monitoring around existing ventilation facilities in Sydney shows that these have no significant impact on local or regional air quality. See our air quality fact sheet for details.


WestConnex uses state-of-the-art ventilation and tunnel design to meet stringent air quality standards in the tunnels and the surrounding community.  Filtration is not used in other road tunnels in Australia and is not needed as it would not provide any measurable improvement to the air quality in the surrounding community. 

Monitoring air quality during operation

All Sydney road tunnels have management plans that involve 24-hour-a-day monitoring of tunnel air quality to ensure they are complying with independent pre-determined guidelines for in-tunnel air quality. 

Under the Conditions of Approval for the M4 East and New M5

  • Local (ambient) air quality will be monitored for at least 12 months before the tunnel opens to traffic and for at least two years after opening. 
  • Air quality inside the road tunnels will be monitored to ensure strict standards are met. 
  • Monitoring results are publicly available and independently audited.

Air quality monitoring for the M4 East project corridor can be viewed online. For more information about tunnels and air quality visit Roads and Maritime Services’ website.

Understanding local air quality

During the planning and assessment phase of WestConnex projects, we undertake air quality monitoring in areas near the project corridor to measure current air quality.

This air quality monitoring information is supplemented by data collected from other monitoring stations operated by NSW Department of Environment and Heritage, and is used in developing the Environmental Impact Statements for WestConnex projects.

Monitoring methodology

Air quality specialists have been commissioned to operate and maintain the monitoring network to Australian standards and guidelines.

Specific pollutants are monitored and reported against the National Environment Protection Measure (Ambient Air Quality). Meteorological conditions are also monitored locally to see their effect on air quality.

For more information, see Ambient air quality monitoring methodology and criteria - October 2015

Air Quality Audits

Audits are required to occur on our projects, and for air quality, these audits focus on the air quality monitoring which is undertaken. The requirements for auditing are detailed within the Infrastructure Approvals issued to the projects, with the auditors typically required to be independent or external auditors. 

Air quality audit reports are provided below.

Monitoring results

Key results from the monitoring of air quality during the planning and assessment phase of the M4 East, New M5 and M4–M5 Link are listed below:

Key results of ambient air quality recorded at the monitoring station at St Peters Street, St Peters are listed below: