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Climate change and the goal of a sustainable, net zero emission economy are leading every industry to rethink its use of resources. As a carbon-intensive sector, transport is a key part of this transition. Operationally, rail is already recognised as a low-carbon option for mass transit – accounting for 8% of motorised travel and 7% of freight, but only 2% of transport energy use (International Energy Agency, 2019). But the construction of rail infrastructure continues to rely heavily on carbon intensive materials such as steel and concrete. So, given we want rail to continue to grow, how can the sector decarbonise its infrastructure?
We have explored this question with the Copenhagen Metro Company (Metroselskabet) to see how far low carbon, reusable, recyclable and biodegradable materials could replace the carbon-costly norms. Specifically, could a natural, sustainable, recyclable material like timber reduce the carbon footprint of station design?
The low-carbon, high timber station
Obviously, to be practical, timber would have to meet the tolerances, durability and fire safety of conventional materials. In rail infrastructure, the use of timber is usually limited to the architectural features, while concrete and steel form the core structural components. Our designs envisage a wider role for timber and confirmed that – either on its own or in combination with concrete – it could indeed deliver the structural performance that station design demands. To be a viable alternative, however, it would have to meet more than structural criteria.
Our main motivation for exploring the use of timber was environmental. Against a baseline of a concrete-only structure, the inclusion of timber reduced embedded carbon by as much as 50%, a saving of up to 150,000kg CO2e. Timber also offers advantages beyond carbon reduction: its lighter weight allows for safer, faster and easier construction. Materials suppliers and construction contractors also confirmed their ability to make timber rail station design a reality.
Safe performance?
Of course, material change brings new risks. Water damage and fire are the most obvious concerns when designing with timber. We explored three different timber/concrete composite designs, each offering a level of protection from water that would underpin a design life of 100 years or more. We also looked at two key fire scenarios – fire on the train and fire in the station itself – and for each scenario, we considered both the performance of exposed and encapsulated timber. Our study of a small sized station, demonstrated that a fire resistance of 90 minutes was achievable. One caveat: the flexible nature of a timber structure creates challenges for stations that use platform screen doors, due to the required tolerances, although the study indicates these challenges can be overcome, with the right combination and integration of materials.
An appealing experience
The quality of the passenger experience will determine whether more people shift from other, more carbon intensive transport, to rail. The inclusion of timber in station design can help set the tone of that experience, creating a warmer, more welcoming aesthetic. It results in appealing, human scale architecture, featuring finer building elements rather than large industrial elements. New manufacturing methods in the timber industry also allow for detailing, adding texture and interest to station designs.
A circular material
The reuse and recycling of timber are central to its potential as a net zero material. Our design was modular, allowing for the easy replacement of any element and, in time, the structure itself. This approach also allows for the sustainable repurposing or recycling of assets as part of a circular economy approach. Timber used in previous generations of rail infrastructure indicates the way forward. Recycled timber sleepers already feature in many gardens and public spaces. There are many more potential applications once we have committed to reusing natural materials. We are expanding our exploration to look at timber metro viaduct as the next step in carbon reduction
Steps on a journey
We believe this was a timely and valuable study. Certainly, the challenge of net zero transport requires that we test a wider range of materials and approaches to the transport infrastructure we depend on.
Achieving net zero rail will take a systemic approach, building on incremental gains across the whole rail ecosystem and its lifecycle. Stations are, of course, only one element of that system. But our study has demonstrated that, if reimagined, station design can contribute to this goal. There are other possibilities for more sustainable infrastructure, from depots and canopies to pedestrian bridges and viaducts. In our work on projects such as Cityringen, HS2 Interchange and New York’s Fulton Transit Centre, we are also reducing the energy demands of stations. All small steps. All incremental gains. But all essential on the journey towards smarter, more sustainable rail.