7 Aug 2014
The NSW Government's Advisory Committee on Tunnel Air Quality released its 'Initial report on tunnel air quality' on Wednesday 6 August 2014. The full report is available here.
NSW Government agencies have more than two decades' experience in assessing and operating long motorway tunnels. Sydney has five lengthy motorway tunnels with significant ventilation systems incorporating stacks
to manage vehicle emissions. These tunnels, and the years in which they opened, are:
* Sydney Harbour Tunnel – 1992
* Eastern Distributor – 1999
* M5 East – 2001
* Cross City Tunnel – 2005
* Lane Cove Tunnel – 2007
Community groups have raised concerns about major tunnel developments over the years partly because of the potential impacts on air quality. In response, successive NSW Governments have subjected Sydney's road tunnels to detailed environmental assessment prior to approval.
The M5 East, Cross City and Lane Cove tunnels are required to undertake extensive monitoring of in-tunnel air quality during operation.
The effectiveness of the stacks in dispersing tunnel emissions from the M5 East, Cross City and Lane Cove tunnels has also been measured as part of separate air quality monitoring programs, which have demonstrated that nearby residents experienced little, if any, increase in exposure to vehicle emissions.
Community confidence in the management of air quality within tunnels, as well as preserving local ambient air quality, is critical to the acceptance of road tunnels as an effective traffic and transport solution. This will be particularly important for Sydney's NorthConnex and WestConnex motorway projects, as the associated road tunnels are likely to be the longest in Australia.
The NSW Government, therefore, established an Advisory Committee on Tunnel Air Quality – chaired by NSW Chief Scientist & Engineer, Professor Mary O'Kane – to provide a 'wholeof-government' understanding of the scientific and engineering issues informing road tunnel ventilation design and operation based on NSW, national and international experience.
In this, its Initial Report, the Committee presents information on the design, assessment and operation of road tunnels; describes how the application of current knowledge can be used to make informed decisions regarding the design and operation of road tunnels; and identifies additional work that is recommended to improve decisions regarding the design and operation of road tunnels.
Up until now, approval conditions and requirements placed on one tunnel project have formed the starting point for the next, with the added inclusion of any precautionary controls to address emerging issues. However, a fresh approach is required for Sydney's newest road tunnel projects to address:
* Community concern as to whether air quality criteria properly address vehicle emissions
* Changes to vehicle technologies that, while reducing the magnitude of vehicle emissions, have also altered the composition of those emissions
* Experience from the Lane Cove and Cross City tunnels that has shown that the ventilation systems are over-designed and that the approval conditions have resulted in inefficient operating regimes.
While motor vehicles remain a significant source of air pollution in Sydney, stricter emission standards and improved fuel quality have resulted in substantial reductions in pollution in the past two decades and, by national and international standards, the city's overall air quality is generally good.
The Committee called for a review of the up-todate science literature, which concluded emissions from well-designed road tunnels cause a negligible change to surrounding air quality, and as such, there is little to no health benefit for surrounding communities in installing filtration and air treatment systems in such tunnels.
Outside Australia almost all road tunnels use portal emissions.
Reductions in emissions has reduced the need for ventilation stacks, and it has become possible to meet both in-tunnel and outdoor air quality requirements using portal emissions alone for some or all of the time. However, in urban areas portal emissions are often supplemented by theuse of stacks, which are seen as a precautionary measure – providing flexibility and resilience in the ventilation system design.
Despite it being common practice internationally to allow portal emissions, operating conditions have been set for the M5 East, Cross City and Lane Cove Tunnels requiring all emissions be expelled through stacks, which requires significant energy use and, during periods of low traffic, may deliver little appreciable environmental benefit.
The Committee therefore recommends that further work be undertaken in three areas to improve decisions regarding the design and operation of road tunnels:
1. Provide information and make recommendations on the assessment and management of portal emissions to improve ventilation system efficiency, reduce overall environmental impacts and provide appropriate protection of the air quality for tunnel users and the community in the vicinity of the tunnel portals. This should include exploring the potential for:
a. optimising portal design on new tunnel projects to maximise dispersion and minimise impacts through the use of physical or computer models (eg wind tunnels or computational fluid dynamics)
b. an investigation of the potential for partial portal emissions at an operating Sydney tunnel without increasing nearby residents' exposure to vehicle emissions.
2. Research, develop and make recommendations on in-tunnel NO2 limits that would provide an appropriate level of protection in the medium to long-term. At the present time an appropriate level of protection from the effect of all road vehicle pollutants in-tunnel is provided through a combination of the existing CO and visibility limits. However, as the composition of vehicle emissions continues to change as emissions decrease, the
addition of a duly considered NO2 limit would ensure an appropriate level of protection continues in the medium to long-term.
3. Investigate and recommend fit-for-purpose standard methods for monitoring in-tunnel air NO2 levels to improve consistency across projects. Pollutant concentrations are routinely monitored in Sydney road tunnels to manage ventilation systems. Monitoring methods for CO and visibility are well established. Monitoring in-tunnel NO2 levels is a more complex task than monitoring CO or visibility. There are a number of techniques for monitoring in-tunnel NO2 levels. Although standard methods are specified for stack and ambient NO2 monitoring, they do not take into account the specific circumstances of the in‑tunnel environment.