There are large differences in life expectancy and the burden of ill health across the UK, both geographically and between different socioeconomic groups. In order to address health inequalities resources must be directed towards policies and programmes that not only improve health overall, but that also reduce the health gap. One of the difficulties for decision makers, however, is that they often do not know what impact a proposed programme will have on health inequalities, or indeed on overall health. This is a particular problem when the proposed programme is complex, an example being the current School Travel Plan initiative. This particular programme has many potential effects on health, both positive and negative, and these may differ in different areas and in different populations. One approach to predicting the costs and health effects of a health promoting programme is through health economic modelling. These mathematical models attempt to replicate the real world in a simplified fashion, combining evidence from diverse sources in order to estimate the outcome of a proposed course of action. This project aims to develop such a model for the school travel plan programme in order to estimate costs, health consequences and the impact on health inequality.