Abstract
BackgroundModifying 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 methodsThe 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.DiscussionAddressing 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.
Highlights
Modifying transport infrastructure to support active travel could help to increase population levels of physical activity
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
Programme guidance on physical activity and the environment issued by the National Institute for Health and Clinical Excellence (NICE) has drawn attention to the lack of studies examining whether changing the physical environment leads to changes in physical activity
Summary
Overall research design The Commuting and Health in Cambridge study comprises three main elements: 1. A cohort study of travel behaviour, physical activity and wider health impacts in adults who travel to work in Cambridge, using repeated postal questionnaires and basic objective measurement of physical activity using accelerometers. Net change is defined as the average within-subject change in a given outcome measure in the ‘intervention’ group minus the average within-subject change in the ‘control’ group after adjustment for demographic, socioeconomic, geographical, psychosocial and health correlates of travel behaviour at baseline using multivariate regression analysis Change in these outcome measures will be studied over a two-year follow-up period in the majority of the cohort, but owing to the delayed implementation of the intervention it is likely that the greatest impact (if any) of the busway on these outcome measures will occur between the second and third years of data collection, and not between the first and second years as originally intended.
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