Guidance

TAG unit A5-4 marginal external costs

Information on the marginal external costs method in transport modelling and appraisal.

From:
Department for Transport
Published
29 May 2020
Last updated
11 December 2025 — See all updates

Documents

TAG unit A5-4 marginal external costs

PDF, 460 KB, 26 pages

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Details

Information on the marginal external costs method, which is based on the change in various external costs such as congestion, air pollution, noise, infrastructure and accidents. The marginal external costs method is used to estimate the benefits of reducing congestion in the absence of a multi-modal model.

The previous version of this guidance was published in May 2023.

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.

Updates to this page

Published 29 May 2020
Last updated 11 December 2025 show all updates

  1. TAG unit A5-4 updated.

  2. Added forthcoming change: appraisal data update.

  3. TAG unit A5-4 updated.

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

  5. Forthcoming change note removed.

  6. Added forthcoming change notes.

  7. Updated guidance.

  8. First published.

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