The health impact of free bus travel for young people in London: protocol for an observational study

Abstract Background: The extension, in September 2005, of free bus and tram travel in London to people 12-16 years of age and, in September 2006, to people under 18 years is likely to have had a range of impacts with implications for public health. The ‘On the Buses’ project aims to evaluate these impacts using a mixed method quasi-experimental design. This paper describes the protocol for the analyses of quantitative data for the study. Methods/Design: Analyses will be based on routine travel survey and injury data for London, and will primarily entail comparison of pre-intervention to post-intervention change in the target age-group (12-17 years) against the corresponding change in people aged 25-59 years. The main outcome measures will include frequency and distance of all travel, and of active travel; frequency of independent travel, bus use; percentage of journeys <1 km travelled by mode; incidence of road injury, and of intentional injury. We will use conditional fixed-effects Poisson models. Discussion: This quantitative study is part of a larger evaluation which draws on qualitative data, economic evaluation and literature reviews to describe the effect of free bus travel for young people on public health. It will also contribute to methodological development in relation to causal attribution in the absence of controlled experimental evidence, and in the use of routine data sets for assessing the effect of interventions on public health.