INSIGHT, BTS | SUSTAINABILITY - CARBON MANAGEMENT


M5 geological profile and tunnel alignment.


elements can be drilled into for more information, by structural element or material. For example, looking at the relatively high carbon footprint showing up in annulus grout, “which was quite a surprise,” Alun said. He highlighted a small “but significant” point, also on


the dashboard: the common Work Breakdown Structure (WBS) is the same for both the cost and carbon estimates. This also opens the door to the evaluation of scenarios in which a number of design changes can be combined and the impact of them on the carbon (and cost) estimate visualised. This helps to achieve more informed and transparent decision-making. The design teams for our major projects must now


have a Carbon Manager to lead this field, Alun said. Having a dedicated person creates a focal point — for example, for knowledge sharing and inspiration. He added that this, in turn, has led to faster and better progress in carbon reduction.


CARBON HIERARCHY As the design develops, the focus shifts into increasingly more detailed areas, Jon noted. The methodology for reducing carbon is very simple and mirrors the familiar approach in value engineering: focus on the big items first and then systematically work through the other elements. For this reason, it is vital to incorporate carbon management from the earliest stages of design. The carbon management process follows a


hierarchy for emissions, to build — nothing; smarter; or, greener. Alun commented that this echoes safety - eliminate hazards; mitigate; and protect.


Baseline and targets Client


TfL


Norwegian road authority Swedish transport authority Copenhagen City Copenhagen metro


Reduction -45% -55% -60% -50% -50%


Deadline 2030 2030 2034 2035


New lines


Baseline 2022 2020 2015 2019


2024-ish


Notes: The Copenhagen metro baseline is definedas: a new line, built according to the as-built design of the latest sections of the existing metro and using materials which are generally used in construction today.


He said start with the big items, and apply the -step hierarchy, pulling in the innovation work from Jon’s team, stressing the importance of the innovation programme as it has already sifted and developed ideas, feeding them into engineering. Examples include:


● having a shallow alignment, which is ‘not building’ so much deep retaining structures and foundations. Can cut the carbon footprint of a station box by 5%-15%.


● the fire/life safety strategy, developed to ensure trains do not stop between stations. This also can eliminate some intermediate shafts.


● reducing the distance from platform to switch, which saw the initial 29m decrease to 16m after considering train speed in practice. This has led to a smaller station box, less excavation volume, and less material quantities, bringing an all-in 6% reduction. Nerdy, but one of Alun’s favourite examples.


● For ‘build less’ the case of elevated twin viaducts was discussed, by having only one that supports a wider deck platform, one for each track. “It is just really good engineering,” he said.


‘Build greener’ gets a lot of attention, especially


concerning materials. But materials are the last step in the hierarchy, Alun said. The focus is on those that are cement-bearing – concrete and grout – as well as steel. He added that with around 20% of the construction-phase footprint coming from the construction processes, there is a need to also look at construction equipment. While a lot is happening in relation to concrete, he said basic questions are necessary. For example, in a high-quality concrete mix with a low water/cement (w/c) ratio, not all the cement (vital as binder) hydrates. Perhaps less reactive replacements, such as limestone fines, can work well. Market dialogue with materials suppliers was


discussed, and the client realising that specifications might exclude some newer, lower-carbon grouts. He observed that clients often tie the hands of contractors and designers. Setting the same requirements all along a metro line to match only


30 | August 2026


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