The built environment has long recognised the outsize contribution it makes to resource use and climate change emissions. Working out how to change the productive model while continuing to develop and maintain the infrastructure we need has been harder. A 2018 report from the OECD stated the challenge in stark terms, projecting primary material use to nearly double by 2060. For the transport infrastructure sector, designing out waste and pollution, designing for reuse, and regenerating natural systems must be immediate priorities.

Is durability the ultimate design virtue?

This question goes to the heart of what needs to change. For many decades, we have largely designed transport infrastructure to last as long as possible without refurbishment or significant maintenance. Durability works for the single life of an asset, but presents challenges at end of life in recovering materials and elements to keep them in use.   

In the last decade a new paradigm for production and operation has emerged: the circular economy. It focuses on reducing resource consumption, emissions and waste and increasing resilience of assets by designing for materials to remain in use and at their highest value for as long as possible. Although we can see an increasing number of sectors embracing this paradigm, the infrastructure sector is lagging. 

The switch to lifecycle design principles

To keep materials and components in use, we need to design for deconstruction and replaceability right from project inception. Durability has its place, but in the form of longevity of materials, elements and systems. The switch needed becomes clearer when you think in layers. 

The concept of “shearing layers – the 6Ss” was first proposed by architect Frank Duffy in the 1970s and further developed by Stuart Brand in the 1990s. The point of visualising in layers is that they reveal the inter-connection between elements that require maintenance and replacement. For transport infrastructure, which needs to provide reliable long-term daily performance, over-design for durability tends to make elements harder to replace or recycle, and adapt them to changing operational needs.  

We have been using layers to visualise how a circular approach to the design of transport infrastructure could lower replacement costs, preserve resources, and liberate operators to meet changing transport needs without building new infrastructure. Two examples, from road and rail, illustrate today’s wastefulness and tomorrow’s potential if a layer-based approach and circular principles work in combination. 

The power of layers

Think of each layer as a group of elements with similar purpose and rate of change. In the transport infrastructure context some layers are more appropriate for ‘replaceability’, such as lighting and signal systems needing regular inspection and replacement. Others lend themselves better to design for maintenance or repair. Longevity is left to the core layers. 

In the three image carousel below, you can see our take on how layers might look for roads, light rail and metro. 

The layers act as a system as they interact with each other. Designing one layer for durability, for example, rail tracks, affects how quickly train wheels wear. A layers-based approach is an important element of the kind of systems thinking we need to apply in the way we develop, finance, design, construct, operate, maintain and repurpose infrastructure assets. 

The central value of this approach is that it reveals the potential for more sustainable design choices over the entire lifecycle, rather than simply aiming to produce durability at any cost.  

More efficient railway maintenance

Using a layers-based approach helps to plan works in an ordered manner, important given maintenance opportunities are extremely limited. Even minor interventions require a complete shutdown of lines. The layers principle allows proper maintenance inspection and planning programmes to be implemented efficiently. 

For upgrade works, including higher speed rail, where newer, more modern infrastructure such as new signalling systems need to be placed in a very constrained cross section, a layers-based approach can help design far more efficient future maintenance. Examining elements in layers grouped by maintenance strategy allows for planning and designing throughout the life cycle in a systematic way.   

Improving Highways

Today, concrete barriers are commonly used as median crash barriers on our roads. During repaving of the road network, these invariably need to be replaced or raised because the barrier is no longer the correct height for vehicle safety. This can happen on a yearly basis, and the old barriers aren’t reused. 

Highways face a lot of future change: electric and hydrogen powered vehicles, congestion charging infrastructure, connected and autonomous vehicles on the road, etc. Bringing inductive charging to the road network would result in the excavation and repaving of the upper layers of whole networks. Elements must be designed for efficient replacement. Change will be the norm in future – a layered, circular approach will help plan and design for this more efficiently. 

Ready for the future

The era of growth at any cost is surely drawing to a close. Regulatory requirements are beginning to come into play around emissions and resource management, that will have implications for the design choices that shape our transport networks. A layers approach is a timely and powerful tool for accelerating the shift to the sustainably developed and flexible transport networks we all want to see.