A NSW Government website

Tunnel Air Quality

Technical Papers 1 - 9: Key Points

TP01: Trends in Motor Vehicles and their Emissions

Author: NSW Environment Protection Authority

  • Australian new vehicle emission standards are set out in the Australian Design Rules (ADRs) and have been progressively and significantly improved over the last 40 years.
  • The National Fuel Quality Standards have progressively required cleaner fuels to complement the ADRs and enable use of improved emission control technology. Proposed reforms to the Standards are underway, focusing on petrol, because Australia’s petrol is not as high quality as petrol in other Organisation for Economic Cooperation and Development (OECD) countries.
  • Emissions from the in-service vehicle fleet (i.e. the vehicles driven in NSW) have significantly reduced as a consequence of the more stringent emission standards and cleaner fuel.
  • Vehicle kilometres travelled (VKT) are increasing steadily, with passenger vehicle VKT increasing in line with population growth at around one per cent annually, while freight vehicle VKT is growing in line with economic growth at two to three per cent annually.
  • In spite of the increase in VKT, the strong reduction in vehicle emission rates has resulted in significant reductions in total fleet emissions, and these reductions are projected to continue over the next 10-20 years.
  • Heavy duty diesel vehicles, and in particular rigid trucks, are disproportionately high contributors to exhaust particulate matter emissions.
  • As the newer vehicles in the fleet have significantly reduced emissions due to the tighter ADRs, the older vehicles in the fleet built to less stringent standards make a significant and disproportionately high contribution to the total fleet emissions.
  • Fleet composition in terms of both vehicle type and age classes are important factors determining the level of emissions from any specific road corridor.

TP02: Air Quality Trends in Sydney

Author: NSW Office of Environment and Heritage

  • In the Sydney region, carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2) and lead concentrations are consistently well below national standards.
  • Ambient levels of ozone and particles can exceed national standards in the Sydney region, with no definite downward trend in the concentrations of these pollutants apparent.
  • Total emissions of ozone precursors and particles have decreased in Sydney over the last decade despite the growth in vehicle activity, energy consumption, population and the economy.
  • Reductions in on-road mobile source emissions have been significant over the last decade due to improved fuel quality and more stringent vehicle emission standards.
  • Despite reductions in vehicle emissions, transport remains a major source of air pollution in Sydney, being the largest source of oxides of nitrogen (NOx) and CO emissions, and contributes significantly to the total emissions of volatile organic compounds (VOCs) and fine particles.
  • The contribution of motor vehicle emissions to PM2.5 (particulate matter) concentrations in Sydney has reduced from 2000 to 2014; however, motor vehicle emissions remain a significant source of fine particles.
  • Regional modelling for Sydney has indicated that the pattern of motor vehicle emissions is a major factor determining the timing and peak of ozone concentrations in the region.
  • The monitors in the NSW air quality monitoring network operated by the Office of Environment and Heritage (OEH) are situated to meet the requirements of the National Environment Protection (Ambient Air Quality) Measure (AAQ NEPM). The AAQ NEPM specifies that performance monitors measure air quality that is representative of that experienced by the general population rather than peak pollution near an industrial site or busy road.

TP03: Health Effects of Traffic-related Air Pollution

Author: NSW Health

  • Motor vehicles are a major source of air pollution in Sydney and other urban centres.
  • Exposure to traffic-related air pollution is linked to a range of adverse health outcomes.
  • Reducing exposure to traffic-related air pollution will provide public health benefits, including improved cardiovascular and respiratory health, and reduced rates of some cancers.

TP04: Road Tunnel Ventilation Systems

Author: Ao. Univ.-Prof. Dr. Peter Sturm, Graz University of Technology, Austria

  • Road tunnels are an important part of transport infrastructure. Originally, they were built to improve traffic and transport conditions in mountainous regions; however, they are now often built in urban areas to reduce traffic congestion and improve local air quality. As road tunnels create an enclosed space around vehicles, ventilation is required to dilute vehicle emissions to provide a safe environment for tunnel users, and to support smoke dispersion/extraction in cases of incidents.
  • Basic concepts of ventilation have not changed over the last few decades. Traditionally, due to fresh air supply requirements, longitudinal ventilation was limited to shorter tunnels with transverse ventilation used in long tunnels. Improved vehicle emission technology and the construction of twin tube tunnels operated with unidirectional traffic now safely enables the use of longitudinal ventilation systems also for long and heavily trafficked tunnels. All long road tunnels built in Australia over the last 25 years have been designed with longitudinal ventilation systems.
  • In urban areas, complex tunnel systems with multiple slip roads to the surface and interconnections with other road tunnels are a popular means to improve the flow of inner-city traffic. These tunnels require individual project based approaches to ventilation as well as ventilation control, and different or combined ventilation systems might be employed within the same tunnel network.
  • Tunnels in urban areas pose an increased risk of elevated pollution levels in the portal regions and may require management of tunnel air. Internationally, many longer tunnel systems in urban areas use stack dispersion only during peak traffic hours, while during the remaining time, tunnel air is released via the portals.

TP05: Road Tunnel Stack Emissions

Author: Dr Ian Longley, National Institute of Water and Atmospheric Research, New Zealand

  • Road tunnel ventilation stacks work by exploiting the natural mixing of the atmosphere to efficiently disperse air pollutants. This point has been recognised by air quality scientists and pollution engineers for decades, and has led to the widespread adoption of the stack as a means of reducing the impacts of pollutant emissions from many sources.
  • Due to the long history of stacks being used to disperse industrial air pollution, there are numerous validated and extensively used atmospheric dispersion models to predict stack impacts. These models are used by regulatory agencies and research communities. These communities collaborate continuously to improve and update these models.
  • Experience from previous motorway tunnel projects, both in Sydney and in other areas of the world, has demonstrated that air dispersion modelling for tunnel stacks is robust and conservative, and that tunnel ventilation stack emissions result in nearby residents experiencing little, if any, increase in exposure to vehicle emissions.

TP06: Options for Treating Road Tunnel Emissions

Author: Ao. Univ.-Prof. Dr. Peter Sturm, Graz University of Technology, Austria

  • The use of tunnel air filtration systems is not common worldwide and such systems present the challenge of capturing and treating high volumes of tunnel air with very low pollutant concentration levels (compared to industrial applications). This results in high infrastructure, operation and maintenance costs.
  • To date, particulate filtration in tunnels is based solely on the use of electrostatic precipitators. The use of air treatment systems for nitrogen dioxide (NO2) is a rarity and has currently only been implemented in full scale in the Calle 30 Madrid tunnel projects, as an alternative to stack dispersion.
  • Any decision-making process concerning tunnel air management (portal air management as well as air treatment systems) needs to prioritise health-based air quality standards when considering engineering and economic practicabilities, and can only be made at the project level. While an air treatment system for particulates or NO2 may be technically feasible, energy usage is high and it will not lower concentrations of other pollutants. Alternatives such as portal air extraction and stack dispersion may achieve the same outcomes at a reduced cost.

TP07: Criteria for In-tunnel and Ambient Air Quality

Author: Dr Ian Longley, National Institute of Water and Atmospheric Research, New Zealand

  • Ambient air quality guidelines are intended to deal with general population exposure to pollution from various sources, rather than exposure at ‘hot spots’ or the control of individual point sources.
  • In NSW, road tunnel stack and portal emissions are typically assessed with reference to both the NSW Environment Protection Authority’s (EPA) Approved Methods for the Modelling and Assessment of Air Pollutants in NSW and the National Environmental Protection (Ambient Air Quality) Measure (AAQ NEPM). However, the AAQ NEPM sets standards for the total ambient concentration of pollutants from all sources and does not provide a framework for assessing the contribution of individual sources such as a road tunnel stack.
  • In-tunnel air quality criteria are established to protect the safety and health of tunnel users with respect to motor vehicle emissions.
  • There is some degree of international consistency among in-tunnel and ambient criteria.
  • Carbon monoxide (CO) has historically been a good marker for motor vehicle emissions and is the basis of in-tunnel criteria. However, reductions in CO emissions due to improved vehicle technology has advanced more quickly than nitrogen dioxide (NO2) and particulate emission reductions. Consequently, a guideline based on CO alone can no longer be considered to automatically provide the same protection of health for tunnel users as in the past.
  • An appropriate level of protection from the effects of all road vehicle pollutants inside tunnels has been provided through a combination of the existing in-tunnel CO and visibility limits. However, as the composition of vehicle emissions will continue to change as emissions decrease, the addition of an NO2 limit will ensure an appropriate level of protection continues in the medium to long term.
  • There are scientific knowledge gaps regarding the effects of very brief (a few minutes) exposures to high levels of air pollutants on health, and regularly repeated exposures, as occur in road tunnels. This requires an appropriately precautionary approach to standard setting that considers the potential health benefits of a standard and the costs of building infrastructure capable of achieving a standard under all possible conditions (e.g. energy use and capital investment that is not utilised).

TP08: Role of NSW Agencies for Tunnel Projects

Author: NSW Department of Planning , Industry and Environment

  • The NSW Government manages the assessment, determination and compliance of significant road tunnels (and associated ventilation systems) as follows:
  • The Department of Planning and Environment assesses proposals under the Environmental Planning and Assessment Act 1979 (EP&A Act) in consultation with relevant State government agencies. The assessment process is public and transparent, with formal opportunities for agencies, local government and the public to provide comment.
  • Prior to public exhibition of the Environmental Impact Statement (EIS) (for all tunnel projects after WestConnex):
    • The Office of the Chief Scientist and Engineer (OCSE), on behalf of the non-Roads and Maritime Services members of the Advisory Committee on Tunnel Air Quality (ACTAQ), provides a scientific review of a project’s air emissions from ventilation outlets for the Minister of Planning’s consideration.
    • The NSW Chief Health Officer releases a statement on the potential health impacts of emissions from tunnel ventilation outlets informed by the review by the OCSE.
  • The NSW Environmental Protection Authority (EPA) provides technical advice to the Department of Planning and Environment on operational air quality impacts during the assessment of the EIS.
  • NSW Health advises the Department of Planning and Environment on air quality health impacts, including appropriate health assessment methodologies for in-tunnel and ambient air quality during the assessment of the EIS.
  • The OCSE, on behalf of the non-conflicted members of the ACTAQ, provides advice on the technical adequacy and appropriateness of the air quality modelling and impacts during the public exhibition of the EIS.
  • The Department of Planning and Environment may also seek advice from an independent air quality expert during the assessment of the EIS.
  • The Minister for Planning is the approval authority for complex infrastructure proposals, including road tunnels. If approved by the Minister, a significant road tunnel will be regulated by a project approval.
  • The Department of Planning and Environment regulates the construction and operation of the project in accordance with the project approval. These functions are generally delegated to the Secretary of the Department of Planning and Environment (or their nominee) under the project approval.
  • The EPA currently licenses tunnel construction activities under the Protection of the Environment Operations Act 1997 (POEO Act). The EPA will license emissions from tunnel ventilation facilities once the NSW Government initiative, announced in February 2018, to strengthen the approach of addressing air quality issues associated with road tunnels is fully implemented.

TP09: Evolution of Road Tunnels in Sydney

Author: NSW Roads and Maritime Services

The NSW Government has over 25 years of experience in assessing and operating road tunnels, including five tunnels in Sydney that have extensive ventilations systems and stacks.

There have been some important lessons learnt from the assessment, design and operation of these tunnels, including:

  • The modelling and assessment processes for stack emissions are well established, robust and conservative.
  • Emissions from well designed stacks have little if any impact on surrounding communities and, as such, there is little health benefit in installing filtration and air treatment systems.

There are a number of lessons that can be learnt from the construction and operation of the M5 East, Lane Cove and Cross City tunnels to enable future tunnel projects to have an efficient ventilation system:

  • Minimising the gradient of the tunnel
  • Locating ventilation stacks close to entry and exit points
  • Designing entry and exit points to reduce congestion
  • Increasing the clearance height and width of the tunnel.

Continuing research on international best practice has resulted in NSW implementing a nitrogen dioxide (NO2) policy which requires tunnels to be designed and operated to achieve some of the most stringent in-tunnel air quality requirements in the world.