The long lifetime and substantial financial cost of transport infrastructure assets makes planning investment in transport networks an important difficult task. The current economic climate means that infrastructure investment funds are likely to be limited in the near future. This scarcity makes it crucial that those funds which are available are invested wisely in assets which will have a long and useful life rather than in projects which will quickly become irrelevant and obsolete. In response to these challenges, the UK Infrastructure Transitions Research Consortium has developed a Transport Capacity-Demand Assessment Model which forecasts UK transport demand and capacity by all modes over the period 2011-2100, and which should allow decision-makers to be better informed when planning future transport infrastructure investments. This model incorporates interdependencies with models of other infrastructure systems, most importantly energy, and thus explicitly accounts for external influences on and drivers of transportation provision. Initial work on the project focused on the development of and testing of this complex model, which considers road and rail traffic and capacity within and between 144 zones, and air and sea traffic via 28 airports and 47 seaports. The model forecasts passenger and freight transport volumes, and the consequent levels of capacity utilisation, energy consumption and greenhouse gas emissions.

Work has now moved on to using the models to evaluate the impacts of a range of possible future strategies which will affect the usage and development of transport infrastructure networks over the remainder of the 21st century. Because of the high degree of uncertainty inherent in predicting how the world will change over a 90-year period, a scenario-based approach forms the best way to explicitly account for this uncertainty, and to allow consideration and exploration of the various futures which could arise, allowing for both ‘known unknowns’ and ‘unknown unknowns’.

This paper first gives a brief overview of the ITRC modelling approach, focusing particularly on the transport model, before moving on to describe and explain the various future transport strategy options being tested and then to discuss the implications for infrastructure planning of the modelled impacts of these strategies on future transport patterns. These strategies range from ‘decline and decay’, where increasing energy prices and resource shortages suppress mobility, through to technology-driven futures where smooth transitions to renewable fuel sources permit more extensive and efficient transport provision, or where the rapid development of ICT-based alternatives to travel mean that substitutes for travel become increasingly important. Overall, the work should help identify which future transport strategies are likely to be most effective in meeting future transport needs by assessing the relative effectiveness and robustness of the strategies in meeting the challenges posed by a range of possible future socio-demographic scenarios. It can therefore help inform infrastructure planning and ease the transition to a more sustainable transport future.