Ogilvie et al. BMC Public Health 2010, 10:703 http://www.biomedcentral.com/1471-2458/10/703 S T U D Y P R O T O C O L Open Access Commuting and health in Cambridge: a study of a ‘natural experiment’ in the provision of new transport infrastructure David Ogilvie1*, Simon Griffin1, Andy Jones2, Roger Mackett3, Cornelia Guell1, Jenna Panter1, Natalia Jones2, Simon Cohn4, Lin Yang1, Cheryl Chapman1 Abstract Background: Modifying transport infrastructure to support active travel (walking and cycling) could help to increase population levels of physical activity. However, there is limited evidence for the effects of interventions in this field, and to the best of our knowledge no study has convincingly demonstrated an increase in physical activity directly attributable to this type of intervention. We have therefore taken the opportunity presented by a ‘natural experiment’ in Cambridgeshire, UK to establish a quasi-experimental study of the effects of a major transport infrastructural intervention on travel behaviour, physical activity and related wider health impacts. Design and methods: The Commuting and Health in Cambridge study comprises three main elements: a cohort study of adults who travel to work in Cambridge, using repeated postal questionnaires and basic objective measurement of physical activity using accelerometers; in-depth quantitative studies of physical activity energy expenditure, travel and movement patterns and estimated carbon emissions using household travel diaries, combined heart rate and movement sensors and global positioning system (GPS) receivers; and a longitudinal qualitative interview study to elucidate participants’ attitudes, experiences and practices and to understand how environmental and social factors interact to influence travel behaviour, for whom and in what circumstances. The impacts of a specific intervention - the opening of the Cambridgeshire Guided Busway - and of other changes in the physical environment will be examined using a controlled quasi-experimental design within the overall cohort dataset. Discussion: Addressing the unresolved research and policy questions in this area is not straightforward. The challenges include those of effectively combining different disciplinary perspectives on the research problems, developing common methodological ground in measurement and evaluation, implementing robust quantitative measurement of travel and physical activity behaviour in an unpredictable ‘natural experiment’ setting, defining exposure to the intervention, defining controls, and conceptualising an appropriate longitudinal analytical strategy. Background A low level of physical activity increases the risk of obe- sity and many preventable chronic diseases including coronary heart disease, type 2 diabetes and cancer of the colon [1]. Observational studies suggest that two and half hours of moderate-intensity physical activity per week is enough to provide substantial health benefits [2], but most adults in countries such as the UK do not achieve * Correspondence: david.ogilvie@mrc-epid.cam.ac.uk 1Medical Research Council Epidemiology Unit and UKCRC Centre for Diet and Activity Research (CEDAR), Institute of Public Health, Cambridge, UK Full list of author information is available at the end of the article this [1,3]. Increasing the population level of physical activity, particularly among the most sedentary, has been described as the ‘best buy’ for improving public health [4] and is an established priority of health policy [5]. Efforts to promote physical activity have traditionally been directed at ‘high-risk’ individuals and focused on promoting sport, recreation, or health-directed exercise [6]. However, there is limited evidence that such approaches are effective in increasing and maintaining levels of physical activity in the medium-to-long term [7] and no definitive evidence of any upward trend in overall physical activity from surveillance data for © 2010 Ogilvie et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.