TAPAS.network | 2 April 2021 | Commentary | Phil Goodwin

Carbon, the roads programme, and ‘de minimis’ in law

Phil Goodwin


EARLY LAST YEAR the environmental campaigning group TAN, the Transport Action Network, started a legal challenge to the DfT’s second road investment strategy (RIS2), arguing that it breached climate and air quality laws. I was asked to write a witness statement on some technical aspects of this case, relevant to whether the appraisals carried out by Highways England and the DfT gave a proper assessment of their impact on carbon emissions. My colleague Jillian Anable submitted a companion statement with her own focus: both of us were greatly assisted by the work of Lynn Sloman and Lisa Hopkinson of the consultancy Transport for Quality of Life, with whom we have worked on these issues over some years. The witness statements are now published and you can read them here (Witness Statement by Professor Phil Goodwin; Witness Statement by Professor Jillian Anable). 

Here is a summary of mine.

The case, and therefore my statement, do not cover all aspects of the debate about road building and its relationship with carbon dioxide emissions from transport. For legal reasons, the focus is on those aspects of the carbon appraisal that touch on the principle of de minimis, usually translated as ‘the law does not concern itself with trifles’, a legal doctrine by which a court can refuse to consider trifling matters.

De minimis was cited by the DfT as applying in this case. It follows the practice of Highways England to report that the carbon effects of specific schemes are “negligible”, “not significant” and would “not have a material impact”.

My witness statement relates to this de minimis claim. There are four main parts to the argument:

  1. I suggest that not all carbon effects of road capacity expansion have been included in the appraisals;

  2. there is an apparent discrepancy between the evidence provided by DfT and that from Highways England;

  3. the unusual criterion used for ‘small’ does not reflect importance; and

  4. an inadequate treatment of uncertainty especially in the traffic forecasts.

On the first point, increasing road capacity increases CO2 emissions in five main ways:

a. during the construction period itself, notably in land clearance and preparation, embodied carbon used in the production of concrete and other materials, and tailpipe emissions from contractors’ vehicles and other activities;

b. during operation from road maintenance, servicing, lighting etc;

c. from road users during the lifetime of the scheme, particularly the tailpipe emissions of that proportion of its expected traffic that has actually been generated or ‘induced’ by the presence of the road itself, including the effect of changes in traffic speed;

d. consequential effects of the roads on settlement and activity patterns, notably when they enable developments of housing, workplaces and retailing, increasing car-dependent lifestyles, increasing car ownership (and increasing the embedded carbon from vehicle manufacturing) and new patterns of warehousing and freight logistics; and

e. synergetic effects such that the impact of each single road improvement on its own may be small but the combined effects of many, in the context of prevailing transport policies, pricing and management, give a greater total than the sum of their parts.

Elements (a), (b) and (c) above are capable of estimation using standard practice in modelling, though are not always included. The calculation of the size of induced traffic under (c) is a subject of professional debate and there is indicative evidence, based on results from Highways England’s analysis of earlier schemes, that HE’s consultants’ modelling underestimates the scale of induced traffic, especially in the longer term. This arises partly because of the effects in (d), since these are the unmodelled elements of induced traffic. Effect (e) cannot be taken into account by adding up scheme appraisals, because the DfT’s appraisal rules treat each scheme as a separate entity, and do not include the effects of future policies. Thus some but not all of the effects are taken into account in the appraisals. The omitted elements (or those that are only partly included) will inevitably lead to an underestimate of the carbon emitted.

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When we add up Highways England’s separate calculations we see a figure that is over a hundred times larger than the figure suggested as relevant to the programme’s appraisal by the DfT.

Turning to the second point, there is a problem, embedded in the appraisals but only recently noticed.

The total emissions of carbon from RIS2 schemes reported by Highways England in its separate scheme appraisals, when added together, give a number that is roundly 100 times greater than that suggested by the DfT as relevant to appraisal of the effects of the programme as a whole (though remembering that the HE figures do not themselves take account of all the potential effects).

The DfT had not published any assessment of the overall effect of RIS2 on carbon, that is for all the schemes taken together for the whole appraisal period. They had suggested a figure for the relevant amount of CO2 produced by RIS2 of 0.28 million tonnes. On examination, this related to the fifth carbon budget period only (a five-year window), and only included five schemes, the latest to be added to the programme. It did not include the total capital/construction emissions as specified above.

By contrast, Highways England had calculated very much higher quantities, though the total was not declared, only the individual schemes. TAN obtained Highways England’s appraisal summary tables (ASTs), through Freedom of Information requests, for 40 of the 50 listed RIS2 schemes, and these provide carbon emissions by users for the full appraisal period of 60 years, though they also do not include construction emissions. These ASTs are a required part of the appraisal process, summarising the extensive modelling and assumptions. The lifetime user carbon emissions attributed to the 40 RIS2 schemes, without any adjustments, totalled 26 million tonnes. Of these, the emissions for the new schemes most recently added to RIS2 came to roundly ten million.

Thus, when we add up HE’s separate calculations we see a figure that is over a hundred times larger than the figure suggested as relevant to the programme’s appraisal by the DfT – though neither figure includes all five of the categories of emissions listed above.

The third point requires unpacking the criterion used by both the DfT and HE when describing carbon effects to be “small”, “negligible” or “insignificant”.

The estimated carbon emissions – even if they had been correctly calculated – are expressed as a percentage of all CO2 from all sources in the whole economy. This number must inherently look minutely small – a tenth of one percent or less – but this does not sensibly measure the importance of the impacts, and is not consistent with the way in which all other benefits and costs are appraised. Consider if one calculated – say – the total number of jobs generated by a specific scheme, as a proportion of the total jobs in the economy; or the number of minutes travel time saved by a particular scheme, as a proportion of all the time spent on everything in the whole country. They would also be a very small number, but that is never used to dismiss them as insignificant. (I have written before on this question – see the article on TAPAS). By this standard, no initiative to reduce carbon in a local area would be worthwhile but, quite rightly, the Government does not take this view when considering measures to reduce carbon, only applying it to measures that increase it.

On the final point, the way in which uncertainty about the future is treated in the appraisals is not consistent with the alternative forecasting scenarios calculated for the 2018 road traffic forecasts (or indeed the 2015 forecasts) that underpinned the Highways England appraisals of each scheme. A key example is that no scenarios for future traffic levels that would themselves substantially reduce carbon were included as a possible future in the baseline forecasts that underpin the appraisals. Conversely, the one scenario at national level assessing the impact of high levels of electrification of vehicles, unfortunately implied substantial increases in traffic congestion, due to the cheapness of electric vehicles, which reduced the carbon savings from this source.

All this leads to the conclusion that the total impact of the road programme on carbon emissions is substantially larger than has been suggested by DfT, whose de minimis appearance is an artefact of an inappropriate standard of what constitutes ‘small’.

Of course, there are many wider issues than this de minimis issue, not necessarily at stake in the legal hearings, but a proper subject of professional and political concern. These will continue independently of the results of the court case.

Phil Goodwin is Emeritus Professor of Transport Policy at UCL and UWE, and Senior Fellow of the Foundation for Integrated Transport.

This article was first published in LTT magazine, LTT820, 2 April 2021.

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