Abstract
BackgroundMechanisms linking changes to the environment with changes in physical activity are poorly understood. Insights into mechanisms of interventions can help strengthen causal attribution and improve understanding of divergent response patterns. We examined the causal pathways linking exposure to new transport infrastructure with changes in cycling to work. MethodsWe used baseline (2009) and follow-up (2012) data (N=469) from the Commuting and Health in Cambridge natural experimental study (Cambridge, UK). Exposure to new infrastructure in the form of the Cambridgeshire Guided Busway was defined using residential proximity. Mediators studied were changes in perceptions of the route to work, theory of planned behaviour constructs and self-reported use of the new infrastructure. Outcomes were modelled as an increase, decrease or no change in weekly cycle commuting time. We used regression analyses to identify combinations of mediators forming potential pathways between exposure and outcome. We then tested these pathways in a path model and stratified analyses by baseline level of active commuting. ResultsWe identified changes in perceptions of the route to work, and use of the cycle path, as potential mediators. Of these potential mediators, only use of the path significantly explained (85%) the effect of the infrastructure in increasing cycling. Path use also explained a decrease in cycling among more active commuters. ConclusionThe findings strengthen the causal argument that changing the environment led to changes in health-related behaviour via use of the new infrastructure, but also show how some commuters may have spent less time cycling as a result.
Highlights
A shift towards more active travel could bring population health and societal benefits (Beaglehole et al, 2011; Douglas et al, 2011; Statistics Netherlands, 2013)
Higher levels of walking and cycling are positively associated with overall physical activity levels (Sahlqvist et al, 2012) and better health outcomes and may result in reductions in health care costs (Audrey et al, 2014; Jarrett et al, 2012)
Because the main outcome evaluation found positive effects on cycle commuting — with a relative risk ratio for an increase in cycling of 1.34 — but not on walking (Panter et al, 2016)
Summary
A shift towards more active travel could bring population health and societal benefits (Beaglehole et al, 2011; Douglas et al, 2011; Statistics Netherlands, 2013). Environmental interventions have the potential to achieve sustained shifts in population travel behaviour, but there is scientific uncertainty about their effects (Fraser and Lock, 2011; Health Council of the Netherlands, 2010; National Institute for Health and Clinical Excellence, 2008; Pucher et al, 2010). This reflects the lack of evaluation studies and the challenges involved in attributing the observed outcomes to the interventions studied. We examined the causal pathways linking exposure to new transport infrastructure with changes in cycling to work
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