This page is an at-a-glance summary of the current TAG units, and what was new in the last update of each unit. May 2026 updates are highlighted. Clicking on the date of the current version will take you to the unit itself.
I will try to keep it up to date, but for anything vital you should always check DfT’s TAG webpages to confirm the latest position and the full content of the guidance.
DfT’s own log of previous versions of TAG units and their Forthcoming changes is here.
Updated to 8 June 2026.
Jump to:
- TAG units : A1, A2, A3, A4, A5, M1, M2, M3, M4, M5, E1
- TAG general and supplementary guidance: general, supplementary
- TAG databooks, worksheets, summary tables and other spreadsheet files (including AMAT and VECAT)
- TAG software tools
TAG units
Appraisal (A) units
A1 Cost-benefit analysis
| Unit | Title | Previous version | Current version | What’s new |
| A1-1 | Cost-benefit analysis | May 2025 | May 2026 | * 2.3.1 to 2.3.4 (appraisal periods) re-worded, with new precise definition of appraisal period * 2.3.9 (old 2.3.8) (appraisal periods below 60 years) has new text on considering end-of life and residual costs * 2.4.9, 2.4.17 and Table 3 (scenarios) have text added re high/low-equivalent and bespoke scenarios * New 2.7.8 on discount rate sensitivity test per Green Book * New section 2.10 and Annex D on appraising options involving private finance per Green Book * New 3.2.8 to 3.2.16 on economic transfers, specifying that these should be included in the analysis * Minor re-wording, re-ordering and consequential re-numbering [was an April 2026 FC] |
| A1-2 | Scheme costs | May 2024 | May 2025 | * Base year (for both prices and values) updated from 2010 to 2023 * Threshold for requiring QRA (para 3.1.1) updated accordingly from £5m (base cost in 2010 prices) to £7m (base cost in 2023 prices) * Table 7 (OB uplift percentages) has new advice on when the fixed-links rate may be appropriate for active mode schemes |
| A1-3 | User and provider impacts | May 2025 | May 2026 | Reflecting the new approach to values of time for freight journeys [was a Dec 2025 FC]. Updates to: * 4.2.7 (becomes new 4.2.7 to 4.2.9) on the VOTs themselves * 4.2.20 (new 4.2.22) on sensitivity testing * 4.5.1 (new 4.5.1 to 4.5.3) on increasing VOTs over time (also updated to refer to different rates for modelling and appraisal) * 5.1.17 and 5.1.21 on non-fuel operating costs (b1 parameter no longer applies to freight) * 6.3.4 on the urban roads method for JTR (new reliability ratios for freight) |
A2 Economic impacts
| Unit | Title | Previous version | Current version | What’s new |
| A2-1 | Wider economic impacts appraisal | May 2025 | May 2026 | * Section 4.4 (GDP analysis within transport business cases) adds guidance on converting MEC impacts to GDP impacts (new 4.4.8, 4.4.9, Table 5) * New Section 8 (document provenance) [was an April 2026 FC] |
| A2-2 | Induced investment | Nov 2024 | May 2025 | * Clarified and expanded definition of dependent development (DD) (section 3.1 and new 3.2) * Additional guidance on how uncertainty around DD benefits should be considered in the economic narrative (new 3.1.23) * New sensitivity test about the level of delivery of the assumed DD (new 3.5, Box 2 and Appendix C) * Updated cross-references to the revised unit M5.3 (SEM) * Minor edits for clarity and formatting |
| A2-3 | Employment effects | Nov 2024 | May 2025 | * Updated cross-references to the revised unit M5.3 (SEM) * Minor edits for clarity and formatting |
| A2-4 | Productivity impacts | May 2025 | Nov 2025 | Minor correction to 4.2.2 text on ramp-up factors for dynamic agglomeration (ramp-up reaches 1.0 in year 11 not year 10) [Not previously listed as an FC] |
A3 Environmental impacts
| Unit | Title | Previous version | Current version | What’s new |
| A3 | Environmental impact appraisal | Nov 2025 | May 2026 | * 3.2.5 (air quality: impact pathways approach) gains a note advising users of databook table A3.2.2 (concentration-based cost values) to contact Defra for further guidance [was an April 2026 FC] |
A4 Social and distributional impacts
| Unit | Title | Previous version | Current version | What’s new |
| A4-1 | Social impact appraisal | May 2022 | Nov 2022 | * 2.3.15-16 updated re safety benefits of rail interventions * 3.2.13 updated willingness-to-pay quality-adjusted life years (WTP-QALY) value * 3.2.18 Changed method of growing absenteeism values. [was an April 2022 FC] |
| A4-2 | Distributional impact appraisal | May 2023 | May 2024 | Noise: New 3.4.10 about potential differences in affected-population estimates between the DI method and the noise valuation workbook method |
| A4-3 | Place-based analysis | n/a | Nov 2022 | New unit |
A5 Uni-modal appraisal
| Unit | Title | Previous version | Current version | What’s new |
| A5-1 | Active mode appraisal | May 2020 | Nov 2022 | Update to cycling diversion factors |
| A5-2 | Aviation appraisal | Nov 2023 | May 2025 | 3.3.3 Updated to reflect carbon price assumptions for aviation emissions under CORSIA being included in the Databook |
| A5-3 | Rail appraisal | May 2025 | Nov 2025 | Table 5 performance-related demand uplift factor updated to refer to PDFH v6.1 (was v6) [was an Oct 2025 FC] |
| A5-4 | Marginal external costs | May 2023 | Nov 2025 | 2.4.7-9 revised to clarify when and how to use databook Tables A5.4.2 to A5.4.4, depending on whether the analysis needs an average impact across the week or a breakdown by time of day and day of week [was an Oct 2025 FC] |
| A5-5 | Highway appraisal | Possibly Oct 2013 | Jan 2014 | [not recorded here] |
Modelling (M) units
M1 modelling principles
| Unit | Title | Previous version | Current version | What’s new |
| M1-1 | Principles of modelling and forecasting | Jan 2014 | May 2024 | General refresh and expansions, including: * Expanding section 1.1 to cover broader purposes of transport modelling and forecasting * Clarifying the key concepts and principles (sections 2, 3, 4, and 5) * Updating figure 1 (the standard transport model structure) * Adding explanation of multi-modal vs uni-modal approaches * Adding re use of ABM (section 4) * New section on modelling active travel and new mobility (section 4) * Changing the term ‘mitigating risks’ into ‘quality assurance’ (sections 4 and 5) and expanding guidance on quality assurance * New section on reporting requirements and potential checks / reviews * Minor clarifications throughout [was an April 2024 FC] |
| M1-2 | Data sources and surveys | May 2020 | May 2024 | Restructuring, plus general update and clarifications. Including: * Adding re new data sources and their use cases * Updating and correcting advice and references on existing data sources * Clarifying advice on the suitability and quality of data * Minor clarifications throughout [was an April 2024 FC] |
M2 Demand modelling
| Unit | Title | Previous version | Current version | What’s new |
| M2-1 | Variable demand modelling | May 2024 | Nov 2025 | * 5.6.14 and 6.4.41 corrected to align with the May 2024 revisions to the recommended JT elasticity ranges for realism-testing * Appendix B (VOTs for income segmentation) updated to reflect the changes to the Databook’s income-banded VOT tables [were Oct 2025 FCs] |
| M2-2 | Base year matrix development | n/a | May 2020 | New unit [Note: unit M2-2 did not change in the May 2024 updates] |
M3 Assignment modelling
| Unit | Title | Previous version | Current version | What’s new |
| M3-1 | Highway assignment modelling | May 2024 | May 2026 | * Removed 2.8.8 advice to double the OGV VOTs, reflecting the new approach to values of time for freight journeys [was a Dec 2025 FC] * C.1.9 (other guidance sources) removed reference to NH microsimulation guidance |
| M3-2 | Public transport assignment modelling | May 2020 | May 2024 | Restructured and expanded. Including new or additional advice on: * The role of PT assignment in the overall model structure * Aspects of model development * Calibration and validation * Convergence * Reporting requirements [was an April 2024 FC] |
M4 Forecasting
| Unit | Title | Previous version | Current version | What’s new |
| M4 | Forecasting and uncertainty | Dec 2025 | May 2026 | * New advice that interim updates to uncertainty guidance will be published online * 4.2.3 (envelope of scenarios) wording corrected * 8.3.1 (EDGE) footnote 5 updated to say that EDGE results, rather than EDGE itself, will be made available [was an April 2026 FC] |
M5 Advanced modelling techniques
| Unit | Title | Previous version | Current version | What’s new |
| M5-1 | Modelling parking and park-and-ride | Possibly Oct 2013 | Jan 2014 | New in the restructured TAG. Material previously in unit 3.10.7. |
| M5-2 | Modelling smarter choices | Possibly June or Oct 2013 | Jan 2014 | [not recorded here] |
| M5-3 | Supplementary economic modelling | Nov 2024 | May 2025 | Major revision to improve the guidance and reflect latest developments in SEM. |
| M5-4 | Agent-based methods and activity-based demand modelling | n/a | May 2024 | New unit. Provides an introduction to these methods. Illustrates where they could be considered and how they can feed into an evidence base. Not guidance on, or approval for, their use in appraisal. |
Evaluation (E) units
E1 evaluation
| Unit | Title | Previous version | Current version | What’s new |
| E-1 | Evaluation | n/a | Nov 2022 | New unit |
TAG general and supplementary guidance
General guidance
| Title | Previous version | Current version | What’s new |
| TAG Overview | n/a | Jan 2014 | New for the restructured TAG |
| TAG Guidance for the Senior Responsible Officer | Dec 2017 | May 2018 | [Not recorded here] |
| TAG Guidance for the Technical Project Manager | Dec 2017 | May 2018 | [Not recorded here] |
| The Transport Appraisal Process | May 2018 | Nov 2025 | New 2.4.4 and 2.10.13 on climate change adaptation [Was an Oct 2025 FC] |
| Spending Objective Analysis | n/a | Nov 2023 | New document. Guidance on spending objective analysis: assessing options in terms of relative and absolute performance against a proposal’s spending objectives. Covers objective-setting, the long-list and short-list stages, reporting the impacts in the Spending Objective Analysis Statement (SOAS), and the link with evaluation. [Was an Oct 2023 FC] |
| Capturing Local Context in Transport Appraisal: Case Studies | n/a | May 2021 | New (in response to the 2020 Green Book review) |
| The Proportionate Update Process | n/a | Jan 2014 | New for the restructured TAG, but based on previous TAG unit 1.5 ‘The proportionate update process’ (Jan 2014) |
Supplementary guidance
| Title | Previous version | Current version | What’s new |
| Uncertainty Toolkit | Dec 2025 | May 2026 | * New advice that interim updates to uncertainty guidance will be published online * 3.20.2 (envelope of scenarios) wording corrected * Changes to wording of Table 1 (table of indicative impact): references to scale of project removed from the ‘Nature and scale of benefits’ row * Changes to advice on scenario selection (Table 2 and 3.21-3.22) (former 3.20.1-3.20.2, now re-numbered) * Removed the example types of lower-/medium-/higher-impact schemes in 3.32-3.34 (former 3.30-3.32) [was an April 2026 FC] |
| Summary of upcoming changes to uncertainty guidance | 11 Dec 2025 | 28 May 2026 | New section ‘Interim guidance, research and scenario development’ with text on its intended role. Includes reference to a ‘think-piece’, due to be published shortly, on the use of scenarios in transport modelling and appraisal in other countries, other sectors and academia. |
| NTEM sub-models | Nov 2014 | July 2016 | Updated to reflect Tempro 7 |
| Mixed Logit Models | Unit 3.11.5 | Jan 2014 | New for the restructured TAG – was previously unit 3.11.5 |
| Bespoke mode choice models | Unit 3.11.4 | Jan 2014 | New for the restructured TAG – based on previous unit 3.11.4 |
| Land Use / Transport Interaction Models | Unit 3.11.3, June 2005 | Jan 2014 | New for the restructured TAG – based on previous unit 3.11.3 |
| Appraisal of New Modes | n/a | May 2025 | New unit. Presents two methods for addressing the ‘new mode problem’: the own-cost approach (as currently implemented in TUBA) and the alternative mode approach (new). Includes guidance on when to use each of these, and worked examples. [Oct 2024 FC] |
| Appraisal of New Modes – worked examples spreadsheet | n/a | V1.0 (May 2025) | New spreadsheet, presenting the calculations behind the worked examples in the corresponding guidance. [Oct 2024 FC] |
| Supplementary guidance on landscape [monetisation] | July 2021 | Nov 2024 | Updated in line with Nov 2024 Value for Money Toolkit. No substantive change to method. [Note: this is technically VfM (not TAG) supplementary guidance, but is included here for completeness as it relates to TAG processes.] |
TAG databooks, worksheets, summary tables and other spreadsheet files
Databooks
| Title | Previous version | Current / forthcoming version | What’s new |
| TAG Databook | V2.02 (Nov 2025) | V2.03 (May 2026) | Reflecting the new approach to values of time for freight journeys [was a Dec 2025 FC]. Updates to: * Annual Parameters: new VoT uprating series for LGVs and OGVs, based on new source tab ‘VoT7’ * A1.3.1: updated road freight values of travel time; this affects tables A1.3.2, A1.3.5 and A1.3.6 * A1.3.4: updated LGV journey purpose data; this affects table A1.3.3 * A1.3.14: added LGV (services) and removed the b1 parameter for LGV (freight) and OGV * A5.4.2 and A5.4.4: updated MECs Other updates: * Annual Parameters, A1.2.1 and A5.3.1 updated with latest economic data (March 2026 OBR Economic and Fiscal Outlook, ONS 2025 outturn data) * A1.1.1 (discount rates) now includes the Green Book sensitivity test rates * A1.3.1 (VOTs) note added to clarify that these values are uplifted by 1.5% annually for appraisal * A1.3.3 (vehicle occupancies) updated * A1.3.4 (journey purpose splits by vehicle or mode) updated, and new London Underground splits added * A1.3.5 and A1.3.6 (VOTs per vehicle, by time of week) updated accordingly. Notes added as reminder that these values should only be used for modelling, not appraisal. * A1.3.9 (vehicle km by fuel type) updated * A1.3.10 (forecast fuel efficiency improvements) updated. A1.3.11 (forecast fuel consumption parameters) updated accordingly * A3.2 (air quality values) updated with latest Defra figures. Methodological note added to A3.2.2 (concentration-based values) [several April 2026 FCs] |
| Common Analytical Scenarios (CAS) Databook | V1.3 (May 2025) | V1.4 (Dec 2025) | * High and low economy scenarios updated with latest OBR and ONS forecasts and projectsions * Technology, vehicle-led decarbonisation and mode-balanced decarbonisation scenarios updated to reflect new fleet modelling [Was an Oct 2025 FC] [See also the summary of upcoming changes to uncertainty scenario guidance] |
Economic impact workbooks and dataset
| Title | Previous version | Current version | What’s new |
| Functional urban regions lookup workbook | Nov 2019 (webpage says May 2020) | Moved to an MSOA-based (2011 data) approach using similar method to before. Also supplied map in sheet within workbook. | |
| Valuing dependent development workbook | May 2019 | ||
| Wider impacts dataset | V4.2 (Feb 2025) | V4.2 (Feb 2025) (but updated for Dec 2025) | Changed to 2023 base year |
Environmental impacts worksheets / workbooks
| Title | Previous version | Current version | What’s new |
| Air quality valuation workbook | Dec 2025 | May 2026 | Updated to reflect Databook v2.03 (May 2026) [was an April 2026 FC] |
| Local air quality workbook | Jan 2014 | May 2019 | Changed PM10 to PM2.5 to align with Defra guidance on concentration-based measurement |
| Biodiversity worksheet | 17 Oct 2013 | Jan 2014 | Definitive release |
| Greenhouse gases workbook | Dec 2025 | May 2026 | Updated GDP deflator forecasts to reflect Databook v2.03 (May 2026) [was an April 2026 FC] |
| Historic environment worksheet | 17 Oct 2013 | Jan 2014 | Definitive release |
| Landscape worksheet | 17 Oct 2013 | Jan 2014 | Definitive release |
| Townscape worksheet | 17 Oct 2013 | Jan 2014 | Definitive release |
| Landscape monetisation workbook | Dec 2025 | May 2026 | Updated to reflect Databook v2.03 (May 2026) [Was an April 2026 FC] |
| Noise workbook | Dec 2025 | May 2026 | Updated to reflect Databook v2.03 (May 2026) [Was an April 2026 FC] |
| Noise workbook – aviation | Dec 2025 | May 2026 | Updated to reflect Databook v2.03 (May 2026) [Was an April 2026 FC] |
| Water environment worksheet | 17 Oct 2013 | Jan 2014 | Definitive release |
AMAT
| Title | Previous version | Current version | What’s new |
| Active Mode Appraisal Toolkit (AMAT) | 3.02 (Dec 2025) | 3.03 (May 2026) | Updated to reflect Databook v2.03 (May 2026) [Was an April 2026 FC] |
| AMAT User Guide | May 2022 | Optimism bias guidance aligned with unit A1.2 |
VECAT
| Title | Previous version | Current version | What’s new |
| Vehicle Emissions Carbon Tool (VECAT) | 1.01 (Dec 2025) | 1.02 (May 2026) | * Updated Tables 1.3.9 and 1.3.11 with TAG Data Book v2.03 values * Corrected CAS Electric HGV emission calculations to use the CAS energy consumption values * Enabled custom inputs for Electric HGV proportions and energy consumption * Updated CAS Electric energy consumption values to use the CAS forecast values directly instead of pivoting off the base TAG 2015 values |
| VECAT User Guide | n/a | Oct 2025 | New item [Was an Oct 2025 FC] |
Social and distributional impacts (SDI) worksheets
| Title | Previous version | Current version | What’s new |
| Journey quality worksheet | 17 Oct 2013 | Jan 2014 | Definitive release |
| Physical activity (basic) worksheet | 17 Oct 2013 | Jan 2014 | Definitive release |
| Security worksheet [SIs – see also DI security worksheet] | 17 Oct 2013 | Jan 2014 | Definitive release |
| Severance worksheet [SIs – see also DI severance worksheet] | 17 Oct 2013 | Jan 2014 | Definitive release |
| DI Appraisal Screening Proforma | 17 Oct 2013 | Jan 2014 | Definitive release |
| DI accidents worksheet | 17 Oct 2013 | Jan 2014 | Definitive release |
| DI air quality worksheet | Jan 2014 | Aug 2014 | Correction – noise replaced with air quality |
| DI appraisal matrix worksheet | 17 Oct 2013 | Jan 2014 | Definitive release |
| DI noise worksheet | 17 Oct 2013 | Jan 2014 | Definitive release |
| DI security worksheet | 17 Oct 2013 | Jan 2014 | Definitive release |
| DI severance worksheet | 17 Oct 2013 | Jan 2014 | Definitive release |
| DI strategic accessibility worksheet | 17 Oct 2013 | Jan 2014 | Definitive release |
| DI user benefits worksheet | 17 Oct 2013 | Jan 2014 | Definitive release |
| DI output summary worksheet | Not recorded | July 2013 | Release of restructured guidance |
Summary tables
| Title | Previous version | Current version | What’s new |
| Appraisal Summary Table (AST) | May 2023 | May 2026 | Value of business user impacts is broken down into freight and non-freight [was a Dec 2025 FC] |
| AMCB Table | 17 Oct 2013 | Jan 2014 | Definitive release |
| Public Accounts (PA) Table | Jan 2014 | May 2025 | Note on price and value base year updated from 2010 to 2023. (No substantive change to format) [was a Nov 2024 FC] |
| TEE Table | May 2025 | May 2026 | Clarified headers for road freight business impacts (no substantive change) [was a Dec 2025 FC] |
| Carbon Summary Table | n/a | V1.0 (Nov 2023) | New table |
Other spreadsheet files
| Title | Previous version | Current version | What’s new |
| Cost proforma | Dec 2025 | May 2026 | Updated to reflect Databook v2.03 (May 2026) [Was an April 2026 FC] |
| Appraisal Specification Summary Table (ASST) | 17 Oct 2013 | Jan 2014 | Definitive release |
| Optimism bias workbook | Undated (published May 2021) | Undated (published Nov 2023) | Labelling corrected [Was not previously an FC] |
TAG software tools
| Title | Previous version | Current version | What’s new |
| TEMPRO (Trip End Model Presentation Program) | 8.1 (Jan 2023) | 8.1 (Sept 2023) | Addition of traffic growth data, enabling the ‘Traffic growth from the NTM’ function. See release notes. |
| DIADEM (Dynamic Integrated Assessment and Demand Modelling) | 7.0.1 (Nov 2022) | 7.1 (Dec 2025) | * Compatible with Saturn 11.5 and above * Compatible with SATUFE and SATUFF in Saturn 11.6 or above * Compatible with networks using area charging * Enhanced error messages * Bug fixes (see release notes) |
| COBALT (Cost and Benefit to Accidents – Light Touch) | v2.9 (June 2025) | v2.10.01 (April 2026, also dated Jan 2026) | * Reflecting Databook v2.02 (Nov 2025) * Additions to user manual [Was an Oct 2025 FC] |
| TUBA (Transport Users Benefit Appraisal) | 1.9.23 Update 1 (Dec 2024) | 1.10.01 update (June 2025) | * Default base year changed to 2023 * Functionality to calculate non-variable costs (NVCs) related to fuel consumption, to align with updated Unit A1-3 * Enforced use of UTF-8 encoding when generating .OUT output files. [Were Nov 2024 and April 2025 FCs] |
| TUBA economics files | June 2025 | TAG Data Book v2.02, Dec 2025 | Reflecting Databook v2.02 (Nov 2025) [Was an Oct 2025 FC] |
| TAG Data Book v2.03FC, Dec 2025 | Reflecting the new approach to values of time for freight journeys [was a Dec 2025 FC]: * Redefining vehicle type/submodes and purposes for LGVs and business trips * Adding new ‘LGV freight’ and ‘OGV freight’ purposes These changes will be applied across all TUBA economics files, including the CAS files | ||
| WITA (Wider Impacts in Transport Appraisal) | V2.4 (Feb 2025) | V2.5 (Sept 2025) | Reflecting Databook v2.01 (May 2025), including 2023 as default base year. |
| WITA economics file | Dec 2025 | Reflecting Databook v2.02 (Nov 2025) [Was an Oct 2025 FC] |