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HS2 will inevitably have a significant carbon footprint, a function of the manufacture, transportation and installation of materials along its 540km length. But capital carbon emissions can be limited –and operational emissions too.

Less is more Kim Hampton and Terry Ellis

Carbon equates to cost, so there’s a strong financial motive to cut CO2 emissions from HS2 during construction and operation. Mott MacDonald director of sustainability and carbon Kim Hampton and
principal environmental scientist Terry Ellis explain.

HS2 will inevitably have a significant carbon footprint, a function of the manufacture, transportation and installation of materials along its 540km length. But capital carbon emissions can be limited –
and operational emissions too.

The calculations are complex, but HS2 estimates that construction emissions for Phase 1 (London-Birmingham) will be in the range of 5.8-6.1MtCO2e (millions of tonnes of carbon dioxide equivalent) while the first 60 years of its operational phase are expected to result in a carbon saving of 3.0-3.2MtCO2e. This factors in the increasing propotion of electricity from renewable sources to power the trains and a modal shift to high speed rail from private vehicles, which emit more per passenger kilometre.

Before it's too late

Carbon savings accrue across all aspects of a project but they are greatest at the very beginning when the big choices are made. The needs definition and optioneering stages are the best moments to influence the outcome. Designers have to be aware of the implications of their decisions from the start, because they are locking-in impact on an asset that should last 100 years or more. By the time construction starts there is very little scope to change things.

Choosing a railway alignment that avoids the need for bridges, tunnels, embankments and cuttings ought to be cheaper, take less time to build and thus have a lower carbon impact.

While functional requirements cannot be compromised it is often possible to refine standard specifications to allow use of unconventional materials. This can make it possible to use locally sourced or site-won materials, and reduce volumes.

Achieving innovation in the trackform will prove challenging given compliance criteria, which require absolute confidence. But there could still be value in engaging with suppliers to gauge what the market has to offer. Very often, it’s the supply chain that offers innovation.

There isn’t a need for revolution: marginal gains across 540km of trackbed will accumulate to create huge carbon savings. Materials delivery, construction sequencing, plant movements. Pause for thought.

Another factor is time and how it is dealt with by some carbon assessments. It is understood that slab track has an adverse impact during construction, but its lower maintenance and renewal requirements make its whole-life carbon cost align with that of ballast after a hundred years or so.

Doing the right thing

Effective carbon reduction involves maximising the opportunities, however limited they might be, everywhere possible. HS2 has proactively identified areas where its project needs to deliver efficiencies: recycled materials, low-carbon concrete blends, rolling stock weight, spoil, logistics, workforce travel. They are very forward thinking and have signed-up to the concept that a low carbon focus can deliver cost savings.

Common goals

Carbon is an effective marker for both material and cost efficiencies. Mott MacDonald has developed a software tool called Carbon Portal with a drag-and-drop interface, able to import data from BIM models and incorporating the most comprehensive carbon and cost datasets in the world. It was created with designers in mind, rather than sustainability professionals or QSs. This allows engineers to compare ideas and options, and make informed choices when the scope for control is greatest. Having carbon as the sixth dimension of BIM is incredibly powerful and can make a tremendous difference to the project’s ultimate bottom line.

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