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Guidance

TAG unit M4 forecasting and uncertainty

Transport analysis guidance (TAG) provides information on the role of transport modelling and appraisal.

Updates to this page

From:
Department for Transport
Published:
31 May 2019
Last updated:
28 May 2026
Show all updates

  1. TAG unit M4 updated.

  2. Added forthcoming change on updates to uncertainty guidance.

  3. 'TAG unit M4' and 'TAG uncertainty scenarios: upcoming changes' updated.

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

  5. TAG unit M4 updated.

  6. Added forthcoming change about appraisal guidance updates.

  7. TAG unit M4 updated.

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

  9. Added forthcoming change: accounting for COVID-19 in transport modelling.

  10. TAG unit M4 forecasting and uncertainty updated.

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

  12. First published.

Documents

TAG unit M4 forecasting and uncertainty

PDF, 718 KB, 61 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

This document gives guidance on the analysis of forecasting and uncertainty in transport appraisals.

The guidance is supplemented by the Uncertainty Toolkit.

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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