Background Data and Assumptions Lower Thames Crossing
Case reference EIR2024/01341
Received 16 October 2024
Published 17 September 2025
Last amended 17 September 2025
Request
I am writing to request information under the Environmental Information Regulations 2004. Specifically, I am seeking access to the following materials related to the National Highways' recent Road to Growth report and its accompanying 3-page Economic Assessment:
The full background data and assumptions used in the modelling that supports the claims made in these reports. This includes (but is not limited to):
- Any relevant Appraisal Summary Tables (ASTs),
- Worksheets or data files used in the modelling process,
- The specific values assigned to "freight movements and other factors" as referenced in the Economic Assessment,
- A detailed explanation of the methodology used to determine these values.
Response
Information provided
The full background data and assumptions used in the modelling that supports the claims made in these reports. This includes (but is not limited to):
The "Road to Growth" report was prepared to support the discussion relating to the benefits of the A122 Lower Thames Crossing. The assessments presented within that document were developed as part of a programme of work undertaken to consider the sensitivity of the economic assessments to various factors and scenarios, as set out below in reference to the detailed methodology.
The assured Benefit Cost Ratio (BCR) and present values of costs and benefits provided within the Development Consent Order application are developed in accordance with the Transport Analysis Guidance (TAG) and provide part of the information suite upon which the Secretary of State will make their decision whether to grant the A122 Lower Thames Crossing Development Consent Order.
These values are provided in Table 1.3 'Initial and Adjusted BCRs, central case (£m, 2010 prices and values)´ in the '7.7 Combined Modelling and Appraisal Report - Appendix D - Economic Appraisal Package' PDF which can be downloaded from this folder EIR2024 01341.
They form the basis for the calculation of the BCR of 1.22. All the supporting analysis including appraisal can be found in the Lower Thames Crossing documents on the
Planning Inspectorate website.
The assessments that support the "Road to Growth" document were subsequently prepared using the developing work being undertaken to consider the updated growth scenarios (NTEM 8), then applying alternative scenarios, not included within TAG, with regard to the value of freight to provide additional understanding of the long-term performance of the scheme under different futures.
Further explanation of the Lower Thames Crossing's economic assessments and figures is available in the Lower Thames Crossing economic assessments PDF, on the Lower Thames Crossing website.
Any relevant Appraisal Summary Tables (ASTs)
The DCO ASTs are available in the document titled 'Combined Modelling and Appraisal Report - Appendix D - Economic Appraisal Package: Appraisal Summary Table Report' which is available here.
All supporting analysis and detail in the DCO analysis can be found here.
No AST's were produced for the analysis we did in summer 2023. This is because it was a minor update to reflect updated guidance and undertake wider sensitivity analysis.
Worksheets or data files used in the modelling process
Please see the spreadsheet titled 'Source 2 - DCOv2 Core Option - CS72-CM49 May 22 - 230216 LTC_benefits_allyear_2022prices_undiscounted v3 (all detail)' which can be downloaded from this folder EIR2024 01341.
The report uses results from the DCO process and subsequent sensitivity analysis undertaken in 2023.
The undiscounted benefits of £27bn are the values taken from the DCO results in the spreadsheet.
Please note that although the total benefits add up to over £28bn, they were rounded down to £27bn. This was to reflect Transport Analysis Guidance (TAG) data and model updates during 2023 which gave marginally different benefit values.
The specific values assigned to "freight movements and other factors" as referenced in the Economic Assessment
A detailed explanation of the methodology used to determine these values.
A benefit-cost ratio (BCR) is used to help the government understand a project's potential value for money when compared to other potential investments. It forms part of the economic appraisal. This, in turn forms part of a wider business case which includes strategic, commercial, financial and managerial appraisals.
The Lower Thames Crossing BCR, referenced in the Lower Thames Crossing economic assessments document, was developed using government guidance that considered a range of sensitivity and scenario tests such as predicted changes in traffic flow, project costs and project delivery timescales, and increases or decreases in population and traffic growth, typically over the first 60-years of opening.
To enable projects of different scales and durations to be compared on a like for like basis, the costs and benefits for a BCR are discounted back to a common reference point to give what is termed as 'Present Value' (PV). This means that the benefits of projects with long life spans, such as major infrastructure projects, can be compared with those with shorter life spans, such as an IT upgrade.
Whilst a BCR is an important tool that helps government assess spending priorities it is rare the full range of possible benefits can be monetised.
Given the long life of investment in major infrastructure projects such as the Lower Thames Crossing, in 2023 the project undertook sensitivity analysis to understand how the project might perform under different futures. It used different combinations of population growth, freight value and carbon valuation as versions of possible futures as these are key drivers to the project in the strategic case for the scheme. This work predated the availability of the DfT Common Analytical Scenario approach which it was not possible to model at the time.
Values of freight and other factors
24 different combinations of future forecasts were tested which are termed combined sensitivity tests. A full breakdown of the 24 scenarios can be found in Annex B which can be downloaded from this folder EIR2024 01341.
Traffic Growth
The analysis used traffic forecasts based on the National Trip End Model version 8 and National Road Traffic Projections 2022. Both tests reflected the TAG guidance of December 2022, that the Low and High growth scenarios should use a p value of 4%. The p value represents the proportion of base year demand which is added to, and deducted from, the Core growth traffic levels, to calculate traffic levels for the High and Low growth scenarios.
Freight
In 2022/23 work was commenced by DfT with National Highways outside of the Lower Thames Crossing project to examine the economic value of freight used in traffic modelling appraisals. This built on past work in 2018 and 2019.
This study has not yet been included in formal DfT transport guidelines but results in 2023 suggested that the current values used could be significantly underestimating the cost to freight of delays on the Strategic Road Network. This is of particular importance when evaluating the benefits of the Lower Thames Crossing project given its predicted high freight loadings. How freight is valued is therefore important to understand the sensitivity of value of the project to the economy and in turn the taxpayer.
Annex A which can be downloaded from this folder EIR2024 01341, provides additional background.
This work suggested that the value of freight could be 2.2 to 3.3 times more than the then current TAG guidelines. However as highlighted a more prudent assumption was used to understand the freight sensitivity.
Carbon
Please see the results in Annex B.
The scenarios compared a core value of carbon used in the DCO, as well as a conservative estimate if the costs of carbon rose by 20%.
This information was used in the non-technical report as set out below.
"Recent economic estimates that put a greater value on freight movements and other factors show that there would be a return in benefits nearer to 1.7 and add up to £40 billion to the UK economy over the first 60-years of its lifetime."
The 'return in benefits nearer to 1.7 and add up to £40bn' refers to the results from combined sensitivity test CH1.
This had a BCR of 1.67 (hence the 'nearer to 1.7' text). The key benefits in the core test (CC4) were £27bn and if the Present Value values of the benefits between CC4 and CH1 are compared, the underlying, undiscounted value are c40% higher - hence the 'up to £40bn'.
The benefit was referred to as 'up to' to reflect that forecasts contain a natural level uncertainty, and assumptions were made about different future scenarios and how the value of freight could vary.
The reference to 22/24 scenarios being above 1 refer to the full suite of results seen in the Annex.
Documents
This is National Highways' response to a freedom of information (FOI) or environmental information regulations (EIR) request.
You can browse our other responses or make a new FOI request.