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Guidance

TAG uncertainty toolkit

Toolkit for analysing and presenting information on future uncertainty in the transport system.

Updates to this page

From:
Department for Transport
Published:
19 May 2021
Last updated:
28 May 2026
Show all updates

  1. TAG uncertainty toolkit updated.

  2. Added forthcoming change on updates to uncertainty guidance.

  3. 'TAG uncertainty toolkit' and 'TAG uncertainty scenarios: upcoming changes' updated.

  4. Added forthcoming change: updates to TAG uncertainty guidance.

  5. TAG uncertainty toolkit updated.

  6. Added forthcoming change about appraisal guidance updates.

  7. TAG uncertainty toolkit updated.

  8. Added forthcoming change: spring 2023 data book and guidance updates.

  9. DfT uncertainty toolkit updated.

  10. Forthcoming change to guidance note added, giving details of updates to be made in November 2022.

  11. First published.

Documents

TAG uncertainty toolkit

PDF, 1.35 MB, 69 pages

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TAG uncertainty scenarios: upcoming changes

https://www.gov.uk/government/publications/tag-uncertainty-scenarios-upcoming-changes/summary-of-upcoming-changes-to-uncertainty-scenario-guidance

Details

A toolkit that provides practical information on:

  • the analysis of uncertainty in modelling and appraisal
  • techniques for exploring that uncertainty in the context of future travel demand
  • how to present this data to decision-makers
  • the common analytical scenarios, including narratives and how to apply them proportionately in transport business cases

It supplements TAG Unit M4: forecasting and uncertainty.

A common analytical scenarios databook has also been published.

The previous version of this guidance was released in December 2025.

TAG provides information on the role of transport modelling and appraisal, and how the transport appraisal process supports the development of investment decisions to support a business case.

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