First published 29th October 2013 and to be found via https://www.gov.uk/guidance/transport-analysis-guidance-tag



The link given is the tip of an iceberg.   There is massive sense in analysing transport flows - current ones and potential future ones - to help ensure we move forward with best systems for the future - but my goodness it gets complicated.  As far as I can see, there is no single download link for TAG guidance, and no layman's introduction or tutorial - but then is this something that is of any use or interest to people using the service and supportive of it being tuned?

Can any of our more technical member's summarise TAG?

 
As you suggest TAG, or WebTAG, is massive. Have tried using some of the stuff relating to active travel, hard work or beyond my abilities. I used the value of a life in various health related analyses. I presume it is also used for railway assessment. https://www.gov.uk/government/publications/webtag-tag-unit-a5-3-rail-appraisal-may-2018. The TAG data book https://www.gov.uk/government/publications/tag-data-book is possibly useful to get an idea of the content.
It, or its component parts, are updated on a fairly regular basis.

 
This link seems to give a reasonably useful overview: reasonable depth without getting into the horrific fine detail of methodology:

https://www.gov.uk/government/publications/tag-guidance-for-the-senior-responsible-officer-may-2018

A few observations:
1. Following the guidance should give some credibility to the idea that forecasts for different projects are comparable; it doesn't necessarily lead to  forecasts that are accurate.

2. There is some mention in the guidance of proportionality. That is: small projects should not need the same level of analysis as large, expensive projects. I'm not sure that this principle is followed throughout the guidance.

3. The three-stage appraisal process: SOBC,OBC, and finally full business case tends to lead to a lot of re-work. Although, in theory, each stage is adding more detail, producing more accurate forecasts, it can feel like paying for the same work over and over again.

4. Forecasting demand is based on evidence, but evidence is more abundant for some types of project than for others. For example, most new stations post-Beeching have been suburban stations aimed at commuters (and others travelling into cities), so an evidence base has grown from the outcome of such stations. Evidence for completely new train services and for (say) stations serving leisure destinations is harder to find.

5. The complete appraisal process is laboriously technical, which is why there are consultants who are happy to earn a living from the work. Even so, they sometimes make mistakes, such as double-counting or omitting significant elements of cost.

6. There are basic forecasting techniques that are within the grasp of the keen amateur, needing nothing more than a spreadsheet and data - much of which is published.

7. We all love to suggest new stations and services. It would be a step forward to subject these to a bit of homebrew appraisal (because it's surprising how far/long some ideas float around without any idea existing of whether or not they could be viable).

 
A thread from Bluesky that throws light on another aspect to this perhaps.

Mark


https://bsky.app/profile/joesarling.bsky.social/post/3l7bgo3debh2m