The appraisal of infrastructure in the UK has developed over time to include multiple attributes, sensitivity analysis and even development pathways. The Department of Transport’s WebTAG methodology, for example, is arguably the most comprehensive transport appraisal guidance in the world (Sumner, 2011), including wider economic factors such as agglomeration. Yet even here, the acknowledged ‘system of systems’ interactions with the other infrastructure sectors (energy, water waste and ICT) are largely ignored. This paper develops current appraisal methods into a common multi-attribute cost benefit approach, allowing analysis of proposed cross-sector infrastructure developments as a portfolio economic investment. The methodology is implemented in three stages:

1. Creation of a common appraisal framework, through the introduction of fifteen cross-sector multi-attribute performance metrics and a multi-sector ‘do minimum’ with a consistent extended time frame of 100 years. Monetisation methods are drawn from current UK industry practice where possible and collated under four headings (environmental, financial, social and service).
2. Consideration of proposed cross sector developments as an integrated portfolio, to assess the system impacts of the total vision compared to individual asset appraisal.
3. Creation of infrastructure development pathways to assess robustness to future uncertainty and flexibility, both individually and as part of a dynamically evolving system of infrastructure systems. Pathways are created through application of interdependencies and resource constraints to a spatial options analysis, then assessed against a common sensitivity analysis and an adapted real options ‘in’ projects analysis.

Each stage is quantified through a case study on the ‘Thames Hub Vision’ (Foster+Partners et al. 2011) to analyse the information gain against the additional effort required and to test the methodology on a regional scale.