One of Australia’s largest tollways, EastLink, has been the first to introduce tunnel ventilation on demand to reduce power usage, greenhouse gas (GHG) emissions, maintenance costs and noise.
EastLink is the major north-south transport artery in Melbourne’s east, connecting the Eastern, Monash, Frankston and Peninsula Link freeways.
The 40km road network is the largest privately operated network in Victoria; as well as being Melbourne’s fastest road and safest freeway, with traffic averaging 250,000 vehicles per day.
EastLink’s tunnels – in particular the tunnel ventilation system – are the largest consumer of power within EastLink’s operations.
This has led EastLink to improve the efficiency and sustainability of the tunnel ventilation system with the introduction of tunnel ventilation on demand.
The EastLink tunnels
EastLink has twin 1.6km tunnels, with three lanes of traffic in each tunnel.
The EastLink tunnels protect the environmentally-sensitive Mullum Mullum valley above, reaching a maximum depth of 53m underground (from valley floor and creek bed to tunnel traffic lanes).
The tunnels, which are monitored and controlled from EastLink’s 24/7 traffic control room, have extensive safety systems.
These include CCTV cameras, an automatic incident detection system, fire detection and deluge systems, radio rebroadcast and public address systems, variable speed signs, digital message signs and lane control signs.
There is also an over-height vehicle detection system which automatically deploys physical barriers to stop over-height vehicles from entering the tunnels and causing damage to infrastructure.
The tunnels have a ventilation system which expels and disperses tunnel air (containing pollutants from vehicles’ combustion engines) through 45m high ventilation stacks.
There is one stack per tunnel. This maintains air quality inside the tunnels as well as in the areas outside each tunnel portal.
The ventilation system can also be controlled in the event of a fire in the tunnel – to help contain the fire initially, and then to dissipate smoke after the fire is extinguished by the deluge system.
The original tunnel ventilation system
The original tunnel ventilation system has been in use since EastLink opened in 2008.
It comprises twelve smaller jet fans in each tunnel, and five larger ventilation fans in each stack.
That’s a total of 34 fans across the two tunnels and two stacks.
The jet fans maintain constant airflow in through each tunnel portal, along the length of each tunnel, and towards the base of each ventilation stack.
The ventilation fans draw air up through each stack for expulsion and dispersal well away from local properties.
Higher airflows, and therefore more operating fans are needed to clear the pollutants produced by higher volumes of traffic.
Since EastLink opened, the speed of airflows within the tunnels and stacks has been controlled by switching individual fans on and off.
There was no speed control for any of the fans.
This switching on and off of fans has been controlled by EastLink’s road and tunnel operating system using a simple pre-set program based on time-of-day parameters, with the largest number of fans operating at peak periods (when traffic levels and pollutants are expected to be at their highest levels).
Manual control has also been available from the EastLink traffic control room to override the pre- set program when operators observe conditions that require it.
Night-time tunnel portal emission
In an Australian first, during 2010, EastLink’s tunnel ventilation system licence, issued by the Environment Protection Authority of Victoria (EPA Victoria), was amended following application from EastLink to allow all ventilation fans to be switched off at night, when traffic levels on the road network are relatively low.
Natural air flow, for example as a result of vehicles passing through the tunnels, meant that the low level of pollutants emitted by vehicles during the night can exit via the tunnel portals – keeping the air quality in the tunnels safe while not compromising air quality in the vicinity of the portals.
This mode of operation is known as “tunnel portal emission”.
The EastLink tunnels have operated successfully with night-time tunnel portal emission since 2010, which reduced power usage and GHG emissions. In addition, ventilation system noise was able to be eliminated each night, helping nearby residents.
Upgrading the tunnel ventilation system
While introducing night-time tunnel portal emission delivered a significant improvement in efficiency, there were still issues with operating this traditional type of tunnel ventilation system:
- Only operating ventilation fans at full speed produces higher operating noise levels, is inefficient and maximises electricity usage
- Toggling ventilation fans between fully off and fully on, and only operating fans at full speed, causes wear and tear on components, increases maintenance costs, and reduces lifespan
- Starting up a ventilation fan from fully off to fully on causes a step-change in noise, which makes the early morning start-up more
noticeable for some nearby residents
- Fan control based on simple time-of-day parameters requires monitoring and manual override by the Traffic Control Room in order to respond to times when traffic patterns are different to normal, for example as a result of an accident. This can result in errors.
New variable speed ventilation fans
To address these issues, EastLink recently upgraded the ten large ventilation fans from fixed speed fully off/fully on operation to much more efficient self-regulating or “closed loop” variable speed operation.
To achieve this, new impellers were installed within each of the existing ventilation fan housings, and new variable speed drives were installed to regulate the rotational speed of the new impellers.
The tunnel and road operating system was updated to provide software control over the new impellers and variable speed drives.
The tunnel and road operating system has also been enhanced to provide fully automatic control of the ventilation system.
It does this by monitoring the output of the existing air quality and airflow sensors located within the tunnels, and automatically controlling the operation of all fans, including the speed of each ventilation fan that is operating at any time.
To achieve efficiency of operations, the new automatic ventilation control system is currently being “tuned” during a series of live tests.
During the tuning tests, the optimum combination of operating fans and speeds of operating fans is being identified to achieve specific airflow requirements.
This information is informing the final setting of the parameters that govern the new automatic ventilation control system.
The tunnel ventilation system will respond to the volume of traffic travelling through the tunnels, as well as the vehicle mix, for example the proportion of heavy vehicles with diesel drivetrains.
Increasingly important for the future, the tunnel ventilation system will respond efficiently to increasing proportions of vehicles with hybrid electric/combustion drivetrains and pure battery- powered electric vehicles (BEVs), which will generate less pollutants and reduce ventilation requirements.
Introduction of limited tunnel portal emissions during day time
These improvements to the tunnel ventilation system are enabling a new change to the EastLink tunnel operating licence to be agreed with EPA Victoria.
The change will allow limited tunnel portal emission during day time. Up to 30 per cent of tunnel air will be able to exit via tunnel portals during day time hours, with the remaining 70 per cent dispersed via the ventilation stacks.
This introduction of limited tunnel portal emission during day time will further increase the efficiency of the tunnel ventilation system.
Air quality monitoring
EastLink already has air quality monitors located within the tunnels and within the ventilation stacks, measuring carbon monoxide, nitrogen dioxide, nitric oxide, total oxides of nitrogen, and particulate matter (PM2.5 and PM10).
Airflow is measured at the tunnel portals and within the ventilation stacks.
The previous day’s air quality charts are published automatically on the EastLink website, and quarterly reports are also published on the same page.
To ensure that air quality standards in the local community have not been compromised through the introduction of the changes outlined, additional air quality monitoring is being conducted in the local community.
A temporary air quality monitoring station has been set up in a small park, located in a nearby residential area close to one of the tunnel portals.
The precise location was identified through modelling, to ensure that the air quality results are worst case rather than best case.
This additional air quality monitoring commenced prior to project implementation to determine the air quality baseline, and will continue until EastLink and EPA Victoria are satisfied that air quality standards have not been compromised by the changes.
It was essential to engage with the community about these changes.
Local residents living close to the EastLink tunnel portals were provided with information about the project before it commenced, as well as at subsequent updates.
This included advance notice of the tune-testing of the new ventilation system, some of which needed to be conducted in the evenings at times when the tunnel ventilation system was normally switched off for night-time tunnel portal emission.
Local residents living near the park where the temporary air quality monitoring station is located were additionally informed about the purpose of the station, as well as the rationale for selecting that specific location.
Local councils were also consulted prior to project commencement.
Motorists who use EastLink were provided with advance notice of a series of night-time lane closures in the tunnels, which were needed to install the new tunnel ventilation fans.
The combination of introducing new variable speed ventilation fans, the new fully automatic ventilation control system, and limited tunnel portal emissions during day time provides the following benefits:
- Reduction in electricity usage and power costs
- Reduction in GHG emissions of 6,441 tonnes CO2-e per annum
- Reduction in noise for local residents
- Reduced ongoing maintenance costs
- Longer lifespan for fan components
- Automatic changes to the ventilation system tracking variations to minimise GHG emissions
- Flexibility to efficiently respond to new vehicle types including hybrid electric/combustion drivetrains and pure battery-powered electric vehicles (BEVs)
EastLink has not received any complaints from the community about this project.
EastLink recommends that operators of major road tunnels consider whether similar changes to their tunnel ventilation system might provide community and business benefits without compromising their applicable air quality standards.
A leader in infrastructure sustainability
The GRESB Infrastructure Assessment recently awarded EastLink the top five star rating for the second year in a row. The internationally recognised GRESB Infrastructure Assessment covers the environmental, social and governance (ESG) performance of 160 infrastructure assets located around the world.