Current methods for appraisal of infrastructure projects have been developed to consider multiple criteria, wider economic impacts and uncertainty, yet their focus on standalone projects and sector specific methods ignores the widely acknowledged 'system of system' interactions between infrastructure networks. Here we draw inspiration from real options 'in' projects to build on current appraisal methods, extending the analysis from single projects to cross-sector regional portfolios and finally to temporally differentiated development pathways; quantifying each stage through a case study on the Thames Hub Vision. The result is a system perspective of the investments, including: (i) the emergent effects of infrastructure asset interactions and how these are affected by the timing and order of development; (ii) an understanding of the 'opportunity' value of an investment through its ability to restrict or enable further developments; and (iii) the total required resources and potential environmental outcomes. Through our case study we demonstrate these effects, identifying system effects sufficient to reverse the outcome of the analysis from a net negative, to a net positive result. Furthermore, we show that the enabling effects of an asset on future developments can create impacts an order of magnitude larger than those observed through current individual asset appraisals. Our developments allow the creation of a decision support tool capable of more fully evaluating the effects of infrastructure investments, with a focus on the long-term opportunity provided by development strategies. The work provides a platform for prioritisation of investments across sectors and for highlighting cross-sector effects, thereby encouraging stakeholder engagement and collaboration. Further work is necessary to explore the effects of intrinsic socio-economic uncertainty in the modelling assumptions and feedbacks between investments and future projections, such as population change and economic growth.

Extreme weather events, such as the UK floods of 2007 and cold snap of 2010–2011, stress the importance of infrastructure systems' resilience for business continuity. The interconnected nature of critical national infrastructure and its component parts places demands on the approach used to deal with its subsequent complexity. Recognition of infrastructure as a complex adaptive system has led to the development of an innovative, systems-based methodology for sustainability assessment in the built environment. The methodology consists of a database of causal interactions which, when combined with a process, allows users to produce causal loop diagrams that identify unanticipated systemic behaviour, communicate risks, share knowledge, and identify systemic intervention points that minimise negative consequences and add value in a project context. The approach is applied to highlight the key characteristics of complex adaptive systems that critical national infrastructure exhibits and show how the technique can be used to increase infrastructure resilience and sustainability.

Evaluation of potential infrastructure projects varies from straightforward financial assessment, to explicit methods requiring multi-criteria valuation and uncertainty analysis. All, however, are siloed to their own sector and in many cases the stand-alone project under consideration, ignoring the growing interdependence between the sectors. Here we develop a long-term multi-sector, multi-attribute decision analysis, demonstrated through a case study on the Thames Hub proposal. Uncertainty is assessed through sensitivity analysis, provisioning time-dependency analysis and an adapted real options analysis, to produce bounded valuation of decision pathways. Further consideration of spatial feedbacks is then reviewed through a land-use transport model. The results are brought together to demonstrate a strategic, integrated infrastructure assessment methodology, focused on delivering long-term resilience despite uncertainty.