Frequently asked questions
Understanding air quality around tunnels and how we monitor
Main air pollutants associated with traffic include particulate matter (PM), nitrogen dioxide (NO2), carbon monoxide (CO), polycyclic aromatic hydrocarbons (PAHs), and volatile organic compounds (VOCs).
For tunnel projects, the approval conditions require ambient monitoring of nitrogen oxide (NO), NO2, PM10, PM2.5, and CO.
Since 2001, the condition of approval has mandated continuous monitoring of NO, NO2, PM10, PM2.5, CO, and VOCs in the ventilation outlets. Additionally, annual monitoring of PAHs and speciated VOCs is required.
Residential, commercial and industrial areas, as well as natural events like bush fires all contribute to air pollution. Motor vehicles also add to emissions, contributing 13% of PM2.5 and 55% of nitrogen oxides (which include nitrogen dioxide (NO2) and nitrogen oxide (NO). Other major contributors include wood heaters (50% of PM2.5) and industry (18% of PM2.5). To find out more, read Sydney’s air quality fact sheet.
Even though the number of cars on the road is growing due to population growth, vehicle emissions in the Sydney region have dropped over the past 40 years. The reduction in emissions from motor vehicles are forecast to fall further over the next 10-20 years because of the continued phasing out of older vehicles, more stringent vehicle emission standards, the introduction of a fuel efficiency standard and the uptake of electric and hybrid vehicles. Find out more on our reducing vehicle emissions page.
According to the World Health Organization, Sydney’s air quality is good by national and international standards. This changes during exceptional events, such as bushfires, but generally returns to the good level quickly. See how we compare to the world on our global air quality page.
Air quality in and around road tunnels
Road tunnels can help reduce air pollution by moving vehicles underground and off the roads where people live and work. In a tunnel, vehicle emissions are controlled and dispersed more effectively away from where people are living and working.
Road tunnels also reduce travel time and congestion by removing the number of traffic lights along the journey. Emissions are also reduced as there is less stop-start traffic and sudden braking.
Tunnels can also reduce road grades (steepness) and corners, meaning vehicle engines don’t need to work as hard and so emit less pollutants.
Ventilation outlets are used to disperse vehicle emissions above and away from nearby buildings. Each outlet is custom designed considering local tunnel air flows, terrain, surrounding buildings and weather to ensure effective dispersion under all conditions. Find out more about Types of ventilation.
The exit points of tunnels, also known as portals, can be used to disperse tunnel emissions. Portal emissions are a type of ventilation system widely used internationally for tunnels. Find out more about portal emissions on our types of ventilation section.
Strategies for managing air quality during construction range from monitoring weather conditions, staging activities, using water sprays, using
rehabilitation or stabilisation techniques and adjusting speed limits. These strategies are outlined in each project’s environmental management
plan on its website. You can find these websites on the our projects page.
The height of a ventilation outlet is calculated based on the tunnel’s location and the surrounding urban area. This ensures that the outlet is tall enough so that emissions result in little, if any, change in air quality when they mix down to the ground level. The process of determining outlet height is comprehensive, involving engineering design, environmental modelling, and adherence to regulatory standards. This approach safeguards public health and environment by effectively managing tunnel emissions.
Internationally, filtration systems are uncommon in road tunnels. According to the Advisory Committee on Tunnel Air Quality, well designed tunnel ventilation outlets result in minimal or no increase in nearby residents’ exposure to vehicle emissions. This is demonstrated by motorway tunnels in Sydney and other parts of the world, without filtration.
Consequently, adding filtration and air treatment systems to such tunnels offers no health benefits for the nearby communities. To learn more about this, visit our tunnels and ventilation page. You can also find out more from our Tunnel ventilation and filtration fact sheet.
Ventilation outlets have an essential role in efficiently dispersing tunnel air high into the sky, well above where people live and work. This is achieved through a combination of natural lift and the axial fans inside the outlet that push the warm tunnel air upward. Once in the atmosphere, the ejected tunnel air dilutes hundreds of times as it mixes with the surrounding air before mixing down to ground level. This results in little, if any, change to the quality of the air people breathe. Importantly, these ventilation systems are built to work effectively under any traffic or weather conditions.
Regulations, compliance, and public engagement
The NSW Environment Protection Authority (EPA) regulates air quality and establishes ways of managing and reporting air pollution. Find out more at the NSW EPA website.
Modern tunnel ventilation design ensures the operation of our tunnels meets strict air quality requirements set by the Department of Planning and Environment and the Environment Protection Licence issued by the NSW Environment Protection Authority. Securing approval for significant road tunnel projects in NSW is a robust and transparent process. This process, among the most rigorous in the world, guarantees each project is thoroughly examined and adheres to the strictest air quality standards. Find out more about how tunnel projects are assessed.
Transport for NSW and private operators of planned tunnels must secure an Environment Protection Licence (EPL) for their projects. This licence outlines key conditions related to pollution prevention, monitoring, cleaner production, recycling, and reuse to promote best practices. Visit the NSW EPA website to get further details on regulatory requirements. These regulations ensure the implementation of environmentally-friendly practices in tunnel construction and operation.
Ventilation outlets are typically placed near tunnel exits as this location generally allows them to function most efficiently and effectively. The location of an air quality monitoring station is generally somewhere within or near the project corridor. During a project’s planning approval stage, an Air Quality Community Consultative Committee (AQCCC) helps determine the location of a monitoring station. This ensures a pre-project comparison of air quality which takes the community’s perspectives into account. Find out more about ongoing projects near you on the our projects page. You can also find out more from our Air quality monitoring station fact sheet.
Strategies for the future
In our pursuit of a cleaner environment and healthier air quality, we are dedicated to both the national and state electric vehicle (EV) strategies. At Transport for NSW, we are transitioning over 8000 of the state’s public transport buses to zero emission technology by 2035 in Greater Sydney, by 2040 in Outer Metropolitan regions, and by 2047 in Regional NSW. This transformative shift aligns with the NSW Government’s pledge to reach net-zero emissions by 2050. It not only facilitates more comfortable journeys for our customers, but also contributes to creating more sustainable, liveable spaces for our communities.
As of 2023, Transport staff’s fleet of vehicles is comprised of over 60% hybrid or electric vehicles. Additionally, Transport is committed to procuring 100% EVs for our staff fleet vehicles by 2030.
Motor vehicles primarily produce 2 types of emissions that affect both the environment and health: greenhouse gases and air pollutants. Greenhouse gases are the leading contributors to climate change. While tunnel emissions only account for a small fraction of total vehicle emissions and an even smaller part of all human-made emissions in the state, we actively collaborate with various government agencies to address emissions at their source. Learn more about reducing vehicle emissions.