Towards More Sustainable Road Tunnels in Australia and New Zealand: Recommendations for Practitioners

Introduction

Sustainability is important for many reasons but fundamentally it is not about what we should do for the environment, it is something we must do to preserve our quality of life and of all life on the planet. It is particularly important for road tunnels because compared to a road at grade, a road tunnel has a substantially larger carbon footprint due to the significant efforts required to build it and the nonstop operation of its systems through its life cycle. In Australia and New Zealand, governments have committed to achieving net zero emissions by 2050. Organisations responsible for delivering and operating road tunnel infrastructure will have an obligation to reduce embodied and operational emissions as far as practicable, as the tunnels will exist beyond 2050.

This article is based on a research project commissioned by Austroads, the collective of transport and road agencies in Australia and New Zealand. The research presented in this article was undertaken as the basis for updating the Austroads Guide to Road Tunnels on the topic of sustainability (Austroads 2022a, b, c, d, & e). This research is publicly available here: austroads.com.au/publications/tunnels/ap-t364-22    

In addition, this research was presented as part of the 2^nd International PIARC Conference on Road Tunnel Operations and Safety & VIII Spanish Tunnel Symposium. Further information on this conference can be accessed here: https://www.piarc-tunnels-spain2022.org/  

This article summarises this research by providing a definition for sustainability in the context of road tunnels; how sustainability fits within the lifecycle of a road tunnel; and case studies of sustainability initiatives for energy efficiency, lighting, ventilation and portal emissions.  

Defining Sustainability in Road Tunnel Developments

At the heart of this research was the concept of sustainability. It can be a complex and evolving subject whose definition may vary from country to country, industry to industry and from time to time. Therefore, defining sustainability appropriately in the context of our research ensured that the solutions developed would be fit-for-purpose for tunnels in Australia and New Zealand.

The research identified three related concepts that contribute to sustainability in road tunnel development: sustainability; infrastructure sustainability; and road tunnel sustainability.

According to the United Nations, achieving sustainability is meeting “the needs of the present without compromising the ability of future generations to meet their own needs” (United Nations, 1987).  This is known as an outcome-based understanding of sustainability and is adopted by Infrastructure Australia (IA) (Infrastructure Australia, 2021).  

According to the Infrastructure Sustainability Council (Infrastructure Sustainability Council, 2021) infrastructure sustainability can be defined as “infrastructure that is designed, constructed and operated to optimise environmental, social and economic outcomes of the long term”. This version highlights the need to undertake a life-cycle approach to achieve desirable sustainability outcomes.  

PIARC (2017) highlights the social, economic and environmental principles as the three pillars that will support the development of sustainable road tunnels. However, the sustainability pillars are not independent; they interact with each other. PIARC (2017) describes the interaction between the pillars such that if the:

• economic and social pillars are both addressed, then the process is equitable

• economic and environmental pillars are both addressed, then the process is viable

• environmental and social pillars are both addressed, then the process is bearable.

One measure, or set of measures, for a road tunnel project to be considered truly sustainable is if all three sustainability pillars are supported. However, this is hardly ever the case in practice. For example, construction of a new tunnel may benefit the economy and have social benefits but may not be positive for the environment. The choices made for sustainability are therefore the result of compromise, balancing the pillars using methods including multi-criteria analysis or a societal cost-benefit analysis to quantify and/or weigh the economic, social and environmental effects.  

The Importance of Considering Sustainability in the Context of Road Tunnels

Road tunnels are energy-intensive elements of infrastructure. Their construction demands a large amount of natural resources and material such as cement, aggregate and steel. In use they require continual operation and maintenance and periodic major refurbishments and upgrades. They generate a large amount of carbon during their operation and maintenance phases. Typically, more than 60% of the total embodied carbon and operational carbon of a project is produced during its operational lifetime (Duarte, Cooke and Thomas, 2013).  As road tunnels have a lifespan of around 100 years, any investment in sustainability will therefore have a long-lasting effect.

Compared to a road at grade, the energy used to build a tunnel is greater; but it is still small compared to the life-cycle energy requirements for its operations, as depicted in Figure 1.

How Sustainability Fits within the Life Cycle of a Road Tunnel

The scope to change the sustainability performance of a road tunnel depends on its developmental stage, with options to address sustainability issues becoming increasingly limited as the tunnel approaches further advanced stages of its development.  

The earlier a sustainability initiative is considered during the life cycle of a project, the better the chance it has to be fully coordinated and incorporated into its lifetime. It will also be less costly to implement. The influence on sustainability outcomes for the life-cycle phases of a road tunnel project are:

• Procurement – whether procurement occurs before or after the planning and design phase, the procurement structure can have significant impact on sustainability. The priority for sustainability compared to other requirements such as time, cost and risk, will influence the sustainability outcomes for the full project life cycle.  

• Planning and design – playing the most critical role in tunnel sustainability is the planning and design phase. The impact of this phase on the operation costs, and therefore maintenance, is significant (60 to 80%); this illustrates the significant influence this phase has when applied to the concept of sustainable development (Infrastructure Sustainability Council, 2021). The relative importance of individual life-cycle phases on the cost of tunnel maintenance is illustrated in Figure 2.  

• Construction – during construction, the focus typically shifts to minimising energy consumption and waste and limiting impacts on the environment and community (PIARC, 2017). Many sustainability measures implemented during the construction phase still need to be identified early in the planning and design phase to be successful.

• Commissioning – during commissioning, there is generally less opportunity to improve the planned sustainability measures, as the purpose of commissioning is to validate that the tunnel is operating as designed. At this stage there is limited historical data available to evaluate potential efficiency improvements.

• Operations – the operation of a road tunnel is highly dependent on the design and construction phases that precede its commissioning (PIARC, 2017). Sustainability can still be supported in the operations phase by improving the measures planned and implemented from the design, based on the evaluation of effectiveness in practice (e.g. energy consumption and air quality). Consideration is often given to routine tunnel maintenance, reactive tunnel maintenance, life-cycle maintenance and tunnel services (e.g. electricity and water). Operations is also the stage where retrofitting is extremely difficult and expensive.

Energy Efficiency in Road Tunnel Operations

As just noted, options to further improve sustainability performance are significantly reduced at the operation and maintenance stages. One exception is during tunnel operation, where there are ongoing training opportunities to raise employees’ awareness of sustainable practices. Opportunities to improve sustainability performance are also present when a tunnel undergoes refurbishment. The extent of the impact will depend on the scale of refurbishment or upgrade. To capitalise on these opportunities, new sustainable technologies may be retrofitted to the existing tunnel. These technologies may include new systems (e.g. lighting and ventilation) that are more energy efficient and/or technologies for mitigating pollution from tunnel operations.

In terms of energy efficiency, major contributions to sustainability can be achieved through improvements to lighting and ventilation systems.

For example, the introduction of LEDs allows the lighting level to be tailored to the ambient lighting conditions of the time of year, time of day and weather conditions outside the tunnel. Further savings can be achieved by shade structures at the portals and by appropriate landscaping at the portals. These methods reduce the difference between the external and internal light level, with a consequent lowering of the artificial light required in the tunnel. Renewable sources of power, such as solar, can supplement energy demands.

Most road tunnels in Australia do not allow portal emissions, representing a significant constraint on the design of the ventilation system at the design and planning stages of a tunnel project (Conway, 2017). Outside Australia however, almost all road tunnels have portal emissions. To achieve zero portal emissions, all tunnel air is discharged through tunnel ventilation outlets to achieve ambient air quality environmental standards, which requires pulling air at the tunnel exit portal against the natural direction of traffic flow (piston effect). This requires operation of the tunnel ventilation system 24 hours a day and does not account for the likely reduction of emissions from vehicles built in the future (O’Kelly, 2020) nor the varying use of the tunnel through a given day and week.  

Both the Eastlink Tunnel in Melbourne, Australia, and the Waterview Tunnel in Auckland, New Zealand, have implemented innovative approaches to ventilation, such as managed portal emissions, to improve sustainability.  

EastLink Tunnel (Melbourne, Australia) Ventilation Improvements

By introducing a more energy-efficient ventilation system, the EastLink Tunnel in Melbourne had its air emission licence amended in 2018 to allow for daytime portal emissions in addition to night-time emissions (EastLink n.d.). Two energy-conserving upgrades were supported by the extended emission hours. Shepherd and Monson (Shepherd and Monson, 2021) found that these upgrades reduced the energy used by the ventilation system by 68%, saving approximately 6.2 GWh or 9000 tonnes of CO_2-e per annum. In addition, this halved audible fan noise. The upgrades applied were: (1) variable speed drives on fans, allowing the fans to operate at a more efficient lower speed; (2) an automatic control system, allowing monitoring of the output of the existing air quality and control of the operation and speed of each exhaust fan.

Waterview Tunnel (Auckland, New Zealand) Portal Emissions

The Waterview Tunnel in Auckland, New Zealand allows portal emissions. The conditions of consent for Waterview effectively require performance-based air quality criteria to be achieved at the nearest sensitive receivers to each portal. This enables the effects of dispersion and dilution to be taken in account while still requiring a clearly defined air quality outcome to be achieved (Hannaby and Wright, 2013).

Barriers to Sustainability

Through an extensive literature review and stakeholder consultation, this research identified some of the potential barriers to achieving good sustainability outcomes on tunnel projects. A few examples of these are:

• a lack of political will and policy-driven solutions towards sustainability.  

• a requirement to permit new material usage but no incentives or rewards to do so, meaning suppliers are disinclined to create more sustainable products and contractors can’t be expected to adopt them in competitive bids, particularly if – even if more sustainable – they are more costly.

• sustainability expressed in contract documents as one of many requirements but typically not given significant priority.

• rating systems that can be taken advantage of by adopting unrealistic business-as-usual standards against which to compare sustainability initiatives. To counter this, some jurisdictions have started to specify the business-as-usual standards in their tender processes.

Achieving Sustainability Success

To conclude, this following discussion provides an example of a typical sustainability approach and considerations for a road tunnel project.  

The success of a project in achieving meaningful sustainability outcomes requires:  

• clear commitment and leadership to deliver sustainability outcomes  

• identification of minimum, feasible and effective sustainability requirements; and the embedding of accountability in these requirements  

• contract requirements structured in such a way that the project team and client prioritise sustainability  

• projects managed so that design and construction decisions consider sustainability outcomes, suitable prioritisation to be applied, and sustainability to be integrated across all disciplines and phases of the project  

• a sustainability plan to be prepared and supporting investigations and activities to be undertaken.