Transport analysis guidance

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


This content contains guidance on the conduct of transport studies. The guidance includes or provides links to advice on how to:

  • set objectives and identify problems
  • develop potential solutions
  • create a transport model for the appraisal of the alternative solutions
  • how to conduct an appraisal that meets the requirements of the Department for Transport (DfT)

Projects or studies that require government approval are expected to make use of this guidance in a manner appropriate for that project or study. For projects or studies that do not require government approval, TAG should serve as a best practice guide.

DfT endeavours to keep the guidance up-to-date in light of new evidence and developments in best practice modelling and appraisal methodologies. Changes are released through an orderly release process, giving users early sight of changes and when they are to be released definitively. Users working on longer-term business cases should refer to the proportionate update process when considering incorporating these changes into their analyses.

For users wishing to understand how the new structure relates to previous versions of TAG, a correspondence table (MS Excel Spreadsheet, 24.7 KB) is available. An archived version of the previous TAG site is also available.


This overview provides general introductory 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.

Guidance for the senior responsible officer (SRO)

This guidance is for project promoters and sponsors who manage and oversee those projects as a whole.

It provides knowledge on how the evidence derived from the transport appraisal process can be used to support the transport business case and inform the decision-making process. It introduces the high-level concepts of transport appraisal and modelling, the important outcomes required and the main risks to monitor and manage.

Guidance for the technical project manager (TPM)

This guidance is for technical managers that oversee the detailed modelling and appraisal work.

It provides more detailed knowledge on the key components of the transport appraisal process – including options development analyses and appraisal – describing how the concepts of transparency and proportionality should be applied. Overall, this should enable those managers to programme and manage the deliverables and resources more effectively. This identifies the main outputs expected in transport business cases and provides checklists of those expectations in more detail.

Transport appraisal process

This guidance gives a more detailed description of the transport appraisal process, including more detail on the 3-stage process of option development, further appraisal and implementation/evaluation.

Spending objective analysis

Informs practitioners on how to assess the contribution of options to achieving a proposal’s spending objectives.

Transport appraisal case studies

These case studies show how local context can be captured as part of the transport appraisal process, to make the argument for transport investment that supports local economic growth objectives.

Proportionate update process

This guidance provides an overview of DfT’s process for updating guidance, when guidance is intended to become definitive and how analysts should go about adopting changes to guidance in a proportionate manner.

Guidance for the appraisal practitioner

These guidance documents inform practitioners of best practice in preparing the necessary outputs for the appraisal of transport schemes and policies.

A1 cost-benefit analysis

These guidance documents give advice on the principles of cost-benefit analysis in transport appraisal, the estimation of scheme costs and the calculation of direct impacts on transport users and providers.

A2 economic impacts

These guidance documents give advice on the appraisal of the wider impacts, regeneration impacts, and dependent development impacts, of transport interventions.

A3 environmental impacts

This guidance provides advice on the appraisal of the environmental impacts of transport interventions. It deals with impacts on both the built and natural environment and on people. The environmental impacts covered in this manual are noise, air quality, greenhouse gases, landscape, townscape, the historic environment, biodiversity and the water environment. The guidance discusses the relationship between environmental impact appraisal (as set out in this unit) and environmental impact assessment and the need to tailor the level of appraisal to the stage of development of the proposal.

A4 social and distributional impacts

These guidance documents give advice on the appraisal of the social impacts and distributional impacts of transport interventions.

A5 uni-modal appraisal

These guidance documents give advice on issues specifically relating to cases where only one mode of transport is explicitly modelled. Guidance is provided for active modes (such as walking and cycling), aviation, rail and highway interventions and on the use of marginal external congestion costs to estimate decongestion benefits resulting from mode switch away from car use.

Appraisal worksheets

Worksheets used to present evidence for each impact:

Guidance for the modelling practitioner

This guidance informs practitioners of best practice in transport models that provide evidence for use in the appraisal of transport schemes and policies.

M1 modelling principles

This guidance provides an introduction to transport models, modelling data and forecasting. It aims to help practitioners understand the general principles of transport modelling and DfT’s forecasting approach. It also identifies the main sources of transport data that are available to practitioners developing transport models and address the methods used for gathering data including survey methodology.

M2 demand modelling

This guidance provides advice on the development of variable demand models. This covers scoping the need for such models, their specification, development, calibration and validation, and ensuring fitness for purpose in forecasting.

M3 assignment modelling

These guidance documents give advice on developing, calibrating and validating highway and public transport assignment models. It provides advice on aggregate highway assignment models, for both general and specific purposes, which represent average conditions over the modelled period. It also provides detailed advice on methods for public transport passenger assignment models.

M4 forecasting

This guidance provides advice on using transport models to prepare future forecasts of demand and supply. This includes guidance on the use of DfT’s demand projections in the NTEM dataset. Furthermore, forecasting is, by nature, uncertain, and this unit gives guidance on how various sources of uncertainty should be taken into account throughout the forecasting process.

M5 advanced modelling techniques

This guidance provides advice on using advanced modelling techniques. These techniques include modelling the impacts of parking policies and park and ride schemes and incorporating the impacts of smarter choice initiatives in existing modelling tools.

Guidance for the evaluation practitioner

This guidance informs practitioners of best practice in planning, implementing and quality assuring the monitoring and evaluation of transport schemes.

E1 evaluation

This guidance provides an overview of good practice in planning the evaluation of transport interventions to ensure robust evidence can be collected about the difference that they are making in practice. It is intended to support evaluation planning and stronger business cases for a range of transport interventions in terms of mode, type of intervention (for example, policy, package of measures, programme) and context (local, regional and national).

TAG data book

The TAG data book includes all of the appraisal and modelling values referred to in the guidance in one workbook.

Common analytical scenarios databook

This databook contains assumptions and inputs for modelling the common analytical scenarios outlined within the Department for Transport’s TAG uncertainty toolkit.

Software tools

To support transport business case development, DfT has produced a suite of tools to enable the appraisal of transport policy and interventions. The purpose of these tools is to ensure a consistent approach in transport appraisal, as well as reducing the cost of carrying out the analysis.

Supplementary guidance

This guidance provides further information on more specific areas of modelling and appraisal methods that TAG users may find useful.

Forthcoming changes

Planned updates to TAG, including details of the guidance being updated and planned dates of release in line with the TAG orderly release process.

TAG update reports

These reports describe our approach to updating TAG in 2020 and 2021.

Feedback and contact

Email contact is used to report a problem with TAG or to join our mailing list, which sends notifications when new information is available or when new TAG units are published (this requires your name, your organisation’s name and email address).

Data protection regulations

DfT will use your contact details to send you emails regarding developments to TAG, invitations to engagement events and feedback surveys. Your information will be kept secure and will not be used for any other purpose without your permission.

Find out more about how DfT looks after personal data, your rights, and how to contact our data protection officer.

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Published 29 October 2013
Last updated 30 November 2023 + show all updates
  1. Added spending objective analysis guidance.

  2. Guidance for the evaluation practitioner published.

  3. Added link to forthcoming changes for November 2022.

  4. Addition of TAG unit A4-3, place-based analysis guidance.

  5. Common analytical scenarios databook added. Updated uncertainty toolkit and TAG unit M4 forecasting and uncertainty.

  6. Notification of forthcoming change for November 2021.

  7. Removed TAG forthcoming changes section.

  8. Added research reports and information on forthcoming changes to TAG.

  9. October 2019 forthcoming changes for the active mode appraisal toolkit, functional urban regions, marginal external costs and matrix building published.

  10. Release of April 2019 forthcoming changes to transport analysis guidance, the guidance being altered is: A1.3, A2.1, A3, A4.1, M4, and the data book.

  11. May 2018 WebTAG updates.

  12. TAG unit A1-1, A4-1, A5-1, A5-3, data book, environmental impacts worksheets, advice for the technical project manager and advice for senior responsible officer updates.

  13. Forthcoming changes to wider impact guidance released.

  14. TAG units A1-2, A5-3, A5-4, M4, TAG data book and 'Forthcoming changes' updated.

  15. TAG unit A1-3, TAG unit M2 and TAG data book updates.

  16. Updated forthcoming changes, unit 2-3 and SI NTEM sub models.

  17. Autumn 2014 updates released.

  18. First published.