Should an engineer designing a new road worry about the embodied carbon of a traffic cone? Should they be calculating the carbon sink opportunity of putting a shrubbery in the middle of a roundabout?

Perhaps not, but they should be considering the further maintenance and operation associated with the project and yes – the million dollar question - they should definitely be thinking about the 34 million cars registered in the UK which could drive on the new road.

Traditionally, design and build infrastructure projects have concentrated on just that - delivering a new asset ready for use, and then handing this over for operation. Anything beyond that - maintenance or repair, or the ongoing use of the asset - simply didn’t fall under the remit of the designer.

Over time however, contracts have expanded in scope, and contractors are now often expected to take on the first five or ten years of operation and maintenance to ensure they plan for the future. Any serious ambitions to rethink our approach to infrastructure to reduce carbon also need to take this wider, whole-life approach.

To take one example, when specifying a motorway central reservation with low carbon in mind, a road engineer may well opt for a metal barrier rather than the full concrete block. But if they were asked to think about the use of the road over the next 50-100 years and the maintenance of that central reservation, they might come to a different conclusion. The metal barrier – though lower in embodied carbon – is likely to be replaced more often than the concrete one, each time requiring a lane to be shut down, causing congestion and consequently a more significant whole-life carbon output.

Four major clients and experienced delivery partners working in infrastructure teamed up with Forum for the Future to think about a consistent method of approach for more holistic carbon management. Through the Engineers of the 21st Century programme, The Highways Agency, Network Rail (supported by RSSB), Atkins and Balfour Beatty tasked young engineers from each organisation to develop a way of assessing and managing the whole-life carbon of an infrastructure project. They came up with a carbon framework, a set of guidance principles and methods of assessment to start developing a common approach for carbon management.

Infrastructure projects, such as building or renewing roads or rail tracks, can take years in the design and build stages, involving a vast list of stakeholders and partners. To manage projects of this size, you have to break them down into contractual stages, supplier frameworks, scope of works and so on, all of which lead towards working within preset boundaries. But what we really want to know at the start of a project is ‘what will be the full carbon impact of doing this?’ or ‘which of our three major options would be lowest carbon overall?’

If the scope of infrastructure projects is expanded to include maintaining and using assets as well as building them, the first challenge is to understand what then falls within the full boundary of each project. If you are considering the impact of people driving on a new or improved road, do you need to also consider the embodied carbon of the cars? And when the construction phase causes congestion or diversions on existing roads, or those popular bus replacement services when railways are being maintained – should that be included in the project carbon total as well? And what about the embodied carbon of the sandwiches eaten by the construction workers on the site, or the paint on the white lines that need to be touched up 20 years later – do we really have to include that much detail to get a full picture?

The carbon framework offers general rules of thumb that will help with these tricky questions. It suggests that first, you should consider all carbon caused directly by a project. Once you have drawn the big circle around the full impact of the project, you can prioritise what carbon you will actively manage and, perhaps more controversially, what carbon you can dismiss because either you cannot influence it or because it is insignificant.

The framework sets out three main categories: carbon you will report (all carbon within the boundary of the project); carbon you will manage (significant, controllable and reducible carbon within the boundary); and carbon you will influence (significant, reducible carbon that may be in or out of the boundary).

It is in this influence box that we can start putting some big issues. A client or designer may not be able to control the number or type of cars driving on a road, but they can influence how they drive with smart design and traffic management. And the carbon reductions available from these kinds of interventions are significant.

The objective is really to enable smarter management of carbon. As carbon becomes an increasingly important factor in projects, the first reaction is to grab whatever data is available, apply some carbon conversion factors and set a reduction target. However, as our understanding matures we need to take a step back and think about where we can get the biggest and quickest carbon reductions – moving on from the low hanging fruit to the big, juicy fruit.

We need serious conversations about a project’s overall carbon impact at the early decision and design stage, informed by clear carbon estimates, in order to sensibly plan for lower-carbon infrastructure.