Air quality

We work hard to ensure high air-quality standards are maintained within our tunnels, and in turn our local communities. Our roads are designed to reduce vehicle emissions as much as possible and we continually monitor and report on air-quality levels to ensure we comply with air quality regulations.

You can find the latest air-quality results in the map below.



 Air quality feed locations

The world’s reliance on fossil fuels is slowly changing. In the future, most vehicles will likely be powered by electricity or hydrogen, but right now road transport emissions account for about 12 per cent of global greenhouse gas (GHG) emissions; which are the primary cause of climate change.

It’s why we are vigilant about managing air quality across our motorways as much as we can.

We consistently look for ways to ensure traffic is free flowing in order to minimise air pollution.

In the last financial year, on average, we estimate that our customers saved almost 30 per cent of their fuel use and GHG emissions by choosing our roads over alternative stop-start routes. Customers also save time and have a smoother and safer trip.

Reducing emissions by design

These days when we build a motorway or tunnel we consider the design’s impact on vehicle emissions. For example, the gradient or steepness of the motorway, its alignment and the smoothness of the pavement can go a long way toward reducing vehicle emissions.

We also monitor the local community’s air quality before, during and after construction for any changes.

In Sydney, after opening the WestConnex M4 Tunnels, air quality along busy surface roads such as Parramatta Road improved by more than 10 per cent. The new underground alternative meant a drop in traffic on local streets and less stop-start congestion, reducing emissions in local suburbs. Being one of the cleanest tunnels in Australia of its size, specially designed for low emissions, there has been no worsening of air quality at any monitoring location.

Reducing emissions with traffic management

It’s not only the structure of the road that can reduce emissions, but how a road is managed. Smart roadside technologies such as coordinating the amount of traffic entering the motorway, lane-use management systems that include variable speed limits and information signs that can be activated quickly when needed, CCTV cameras, automatic incident, height and occupancy detection, all work together to help get the best out of a motorway – this includes maintaining free-flowing conditions that help to reduce vehicle emissions.

Managing and reporting air quality

All of our tunnels have ventilation systems that move air into, through and out of the tunnel in a safe and efficient way. A typical ventilation system includes:

  • jet fans to control air movement through the tunnel
  • ventilation fans to draw air into and out of ventilation outlets
  • ventilation outlets to discharge air (sometimes called ‘vent structures’ or ‘stacks’)

Ventilation systems are designed to meet stringent air quality measures, which are reported to and enforced by the relevant environmental authority in each state. We monitor air quality within our tunnels and, depending on the individual tunnel may also monitor ventilation air quality and ambient air quality around tunnel portals.

In Brisbane, we’re using technology to adapt our tunnel ventilation systems to better align with traffic flow and allow air to be released from tunnel portals as well as ventilation outlets during off peak periods. These improvements will reduce energy consumption while allowing us to maintain safe air quality both inside and outside the tunnels.

For more information on how we manage and report on air quality you can download a fact sheet (PDF) or refer to frequently asked questions below.

Note: gradient shown is for illustrative purposes only.


  • What is air quality and how is it monitored?

    Air quality refers to the degree to which air is suitable or clean enough for humans or the environment.

    Transurban uses a range of tools to report on the air quality of its operational tunnels in Melbourne, Sydney and Brisbane.

    Monitoring and reporting requirements vary for different tunnels according to the specific operating and legal requirements. We monitor air quality within our tunnels and, depending on the individual tunnel, may also monitor ventilation air quality and ambient air quality around tunnel portals.  

  • What are air quality standards and does Transurban have to comply?

    Environment Protection Authorities in NSW and VIC, and the Department of Environment and Science in QLD monitor air quality in line with the National Environment Protection (Ambient Air Quality) Measure (NEPM).

    These requirements are passed on to Transurban to comply with through its operating agreements with governments.

    In addition, international best practice standards are set by the Permanent International Association of Road Congresses (PIARC), formerly known as the World Road Association relating to in-tunnel air quality and visibility.

  • How does the design of a road improve air quality?

    A wider and flatter road will result in a smoother journey with less stop-start driving, leading to reduced vehicle emissions. Factors such as road gradient, pavement smoothness and free-flowing traffic all help contribute to improved air quality and are incorporated into the design and operations of our roads. In FY21, on average, our customers saved almost 30% of their fuel and greenhouse gas emissions by choosing our roads rather than alternate stop-start routes.

    Tunnels can also help reduce air pollution by moving traffic off surface roads, near where people live and work, and putting vehicles underground. This is because vehicle emissions can be captured more effectively in a tunnel and dispersed high into the atmosphere, when compared with a road above ground.

    In addition to designing and operating our roads and tunnels in ways that protect air quality, we are testing new technologies aimed at improving air quality. To date, we have tested plant-breathing walls on two Sydney roads to determine their impact on air quality. In Melbourne, we started a trial of air purifying paint on a CityLink wall panel. The paint has the potential to reduce pollutants like nitrogen oxide and nitrogen dioxide, and contains self-cleaning properties, which could reduce maintenance costs and water consumption.

  • Why aren’t filtration systems used?

    The two main types of filtration available are Electrostatic Precipitator (ESP), which removes particles and DeNOx filtration, which removes nitric oxide (NO) and nitrogen dioxide (NO2). While these systems are effective in filtering emissions from industrial sources, where levels of pollutants are higher, they are less effective within tunnels due to the challenges associated with filtering a high volume of air with a low level of pollutants.1

    M5 East trial

    Between March 2010 and September 2011 an Electrostatic Precipitator (ESP) and DeNOx System were trialled in the M5 East Tunnels to reduced haze caused by particles emitted by older diesel trucks. The trial was assessed by both the Commonwealth Scientific and Industrial Research Organisations (CSIRO) and AMOG consultants. Both reviews found removal efficiency of PM2.5, PM10 and NO2 were lower than expected. Both reports recommended that alternative methods be investigated to remove particulate matter and NO2 such as truck fleet upgrades.2

    1. Ao. Univ.-Prof. Dr. Peter Sturm, NSW Advisory Committee on Tunnel Air Quality, Technical Paper 06: Options for Treating Road Tunnel Emissions
    2. Roads and Maritime Services

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