Connect2 is a 138 million investment programme in walking and cycling infrastructure at 79 sites across the UK that provides a unique opportunity to determine the impact of infrastructure provision on walking and cycling and to assess the impact of other interventions including promotional activities. The challenge is to ensure this opportunity is used to fill evidence gaps, assess transferability and influence policy. The aim of this project is therefore to measure and evaluate the travel, physical activity and carbon impacts of interventions to improve the connectivity of infrastructure for walking and cycling. To achieve this aim we have developed an interdisciplinary consortium of eight institutions with expertise in energy, environmental, physical activity, public health and transport research, as well as computerised urban modelling. Our objectives are: (1) to develop and refine measurement instruments and evaluation frameworks for assessing the effects of these interventions on travel activity, physical activity and carbon emissions; (2) to apply these methods in longitudinal population-based studies at a purposive sample of up to six Connect2 case study sites; (3) to determine the likely benefits of additional promotional interventions using a randomised controlled trial at one Connect2 site (provisionally the Road to Nowhere scheme in Glasgow); and (4) to enhance and collate data at all Connect2 sites to develop strategic evaluation measures. Our methodological approach will be informed by the realist approach to evaluation which advocates determining not simply whether an intervention has worked but also understanding why it is effective (or not), in what ways, for whom and in what circumstances. We will therefore collect data on context, mechanisms and outcomes using a longer self complete household questionnaire, to which we anticipate a total of approximately 10,000 useable responses from the main case studies; a shorter user intercept questionnaire, developed in conjunction with Sustrans; and more detailed objective measures from subsets of our study cohorts. The main outputs will be an improved set of measurement and evaluation tools at the strategic and more detailed, local levels, validated using a heterogeneous set of Connect2 case studies; evidence on the impacts of infrastructural and promotional interventions, which will inform policy and practice; and strategic benefit and cost measures which will inform and influence government policy and appraisal of infrastructural interventions. These outputs will have significant generic benefits for central government, local authorities, active travel users and academia.