Guidance

Forthcoming change: appraisal of new modes guidance

Updated 17 October 2024

Description: introduction of guidance on the appraisal of new modes

Unit: new supplementary guidance unit

Change announced: October 2024

Expected release date: May 2025

Description

This forthcoming change provides an overview of new guidance intended to support analysts in the appraisal of new modes, in particular new rail lines or stations, to be released definitively in May 2025. The guidance, in the form of a supplementary unit to TAG, will describe 2 viable methodologies, discuss when it may be appropriate to use each of these, and provide worked examples. An accompanying spreadsheet will be provided with the detailed calculations of the worked examples.

The new guidance is available alongside this forthcoming change. Existing guidance on new mode appraisal in the TUBA ‘General guidance and advice’ document will be removed from May 2025.

Detail

Background

This forthcoming change notifies users of the introduction of supplementary guidance in TAG to be released definitively in May 2025. This guidance provides advice on the appraisal of new modes, with a focus on rail openings such as new lines or stations, and builds upon research by the Institute for Transport Studies (ITS) Leeds for the Rail Safety and Standards Board (ITS Leeds, 2021^{[footnote 1]}, 2023^{[footnote 2]}, as well as a subsequent peer review by John Bates (2023^{[footnote 3]}, to be published).

The guidance identifies 2 approaches that can be used to overcome the ‘new mode problem’; that where a mode is added to the do-something (DS) scenario, there are no observable costs for this mode in the do-minimum (DM) upon which to base a reliable appraisal of the impacts. The benefits and drawbacks of these methods are described, and simplified worked examples (also set out in detail in an accompanying spreadsheet) provide a demonstration of how these approaches work in practice.

Given the relatively novel methods set out in the supplementary guidance, TASM (TASM@dft.gov.uk) welcomes feedback from those using the guidance in practice, and analysts should be aware that there may be minor drafting or technical changes to the guidance displayed in the accompanying guidance or spreadsheet prior to definitive publication in May 2025. However, the fundamental nature of the methodologies displayed will remain unchanged.

Methods for appraising new modes

The guidance provides advice on a new approach to the appraisal of new modes. This approach (the ‘alternative mode approach’), is based on the observed travel choices of users in the DM, considering the change in generalised cost (GC) from one mode in the DM, to the new mode in the DS. Being rooted in credible DM and DS choices (including ‘no travel’), the alternative mode approach generates user benefits without the need to extrapolate the full demand curve to the cost axis.

This new approach is presented alongside the existing ‘TUBA’ methodology (the ‘own-cost approach’), which relies upon the estimation of a ‘pseudo-DM’ level of cost which would suppress trips on the new mode to near-zero, and then applying standard rule-of-half (RoH) calculations to estimate user benefits in the DS.

The guidance sets out the benefits and drawbacks of using each of the above 2 methodologies, when it may be suitable to use each approach, and important further considerations for the analyst. There is no one-size-fits-all way to define the preferred approach for a given scheme, as this will depend upon the context of the scheme, the travel costs involved, and planned modelling approach. Each of the 2 approaches outlined above can be used to provide validation or a sense-check of the other, although noting the need for analysis to remain proportionate. The alternative mode approach relies on (i) the availability of relevant modal diversion factors; and (ii) being able to specify a large proportion of modal utility within generalised cost, leaving as little as possible in the ‘error’ term. By comparison, the own-cost method relies closely on the assumptions implicit in the demand model.

While the new guidance is framed in terms of the addition of new modes, the methods presented can also be used ‘in reverse’ to appraise taking away a mode in the DS.

Additionally, simplified worked examples of the 2 methodologies will be provided to demonstrate their practical application. A spreadsheet will be provided alongside the supplementary guidance (as well as this forthcoming change), which details the underlying calculations. This spreadsheet corresponds to the simplified examples presented in the guidance, and should not be considered a tool for appraisal.

Other guidance and documents

The existing guidance on the appraisal of new modes contained in chapter 12 of the TUBA ‘General guidance and advice’ document^{[footnote 4]} will be removed, given detailed advice on the own-cost approach will now be reflected in the supplementary guidance.

No changes will be made to the TUBA software, which can be applied in the context of either outlined approach.

Where applied in the context of rail closures, the new guidance should be understood in conjunction with existing advice, including Rail closures guidance (2006).

1. Ojeda-Cabral M, Batley R, Johnson D, Rail openings appraisal, November 2021 ↩

2. Ojeda-Cabral M, Batley R, Johnson D, Rail openings appraisal 2, February 2023 ↩

3. Bates J, Peer review of multi-modal appraisal methodology, May 2023 ↩

4. AtkinsRealis and Department for Transport, ‘Transport user benefits appraisal (TUBA): general guidance and advice’, volume 1.9.17, May 2024 ↩