The Green Book Review and what this means for transport business cases

Good business cases are integral to evidence-based decision making. Clearly defining objectives and a case for change, they provide a framework for the development and assessment of alternative options. They set out how the preferred option will deliver value for money. They establish how the intervention will be funded and financed, and how it will be delivered. They are the starting point for ex post evaluation and the lesson learning that comes from this. They promote transparency and accountability. A good business case supports good decision making.

The Green Book is the government’s guidance on business cases. Updated from time-to-time, the Green Book’s history stretches back well over half a century. However, in recent years the Green Book has been criticised as being inflexible and not supporting the development and implementation of interventions necessary to further government objectives such as promoting economic growth in the UK’s less well-off areas. In June 2025 the government published its latest review of the Green Book with the promise that a new version of the Green Book will be available in early 2026. This paper is the TPS’s commentary on the six actions set out in the June 2025 Green Book Review.

Central to this paper is the recognition that for the day-to-day work of most business case practitioners, it is not the Green Book itself that is important but rather it is how it is reflected in the Department for Transport’s (DfT’s) Transport Analysis Guidance (TAG), Value for Money Framework and wider suite of business case guidance. Taking each Green Book Review action in turn, this paper sets out recommendations to the DfT on how it should implement the Green Book Review’s actions in ways that encourage and facilitate practitioners to change their ways of working.

The report was produced by Transport Planning Society’s Governance, Appraisal and Business Case Modelling policy group members Neil Chadwick, Joe Charlesworth, Graham James and Tom van Vuren.

Find the full report below.