We have identified a number of areas where more evidence would be useful to inform policy.
The effects of ‘active travel’ on health
There are plausible grounds for encouraging active transport as a way to increase the levels of physical activity in the population, but our literature review90(see Appendix 8) identified a lack of robust studies
which demonstrate the health benefits of this. A considerable amount of cross-sectional research identifies health gains in those who are active, but to date there is a dearth of studies which demonstrate that changing the amounts of active transport individuals undertake will result in health benefits. Given uncertainties around activity synergy and compensation, and the debate around how much additional activity is needed to produce health gain, particularly for young people, intervention studies are urgently needed to address health outcomes of changes in behaviour. Additionally, given the population
differences in transport mode choice, we need more information about how such interventions are likely to affect different groups in the population.
The effects of different transport modes on the determinants of health
The qualitative data suggested a number of benefits for young people of universal free bus travel that could not be captured through current quantitative measures, including fostering independent travel, fostering a sense of‘belonging’, facilitating social inclusion and providing a rare space to socialise. We have, however, no comparative data on what other modes might provide. Being driven, for example, although having costs in terms of active transport, may be a rare opportunity to talk with parents in a busy day, and walking can provide young people with opportunities for private discussions with friends. Any full assessment of the health effects of transport mode choice for young people would need to incorporate these broader implications of transport mode choice for health, requiring more research on the meaning of transport and well-being in the lives of young people, particularly adolescents who have been relatively under-researched.
This may well require the development of novel methodologies. Travel diary data provide feasible sources for assessing large-scale changes in transport mode, but have limitations in capturing the‘non-travel’ activity related to transport mode use, as illustrated in Chapter 3, where bus travel that is undertaken for the‘fun’ of the journey may be under-recorded in travel diary time. More direct measures of young people’s activity [such as Global Positioning System (GPS) or activity monitors] have their own problems: Mackett and colleagues180report the difficulties in collecting data from large numbers of young people at
a time; managing the large number of data points in analysis and the pragmatic demands on participants of managing the devices.
Maintenance of transport mode change
One causal pathway for which we had limited evidence was that leading to reduced car dependence. The likely impact of transport interventions on sustainability is a crucial issue, and this policy aimed to reduce future car dependency. In general, we found little literature on how far habits changed in adolescence (or indeed later) are maintained in the medium and long term. Despite promising modelling181,182suggesting
that it is possible to change travel habits through changes in environment or policy, and intervention studies with promising results on the possibilities of increasing public transport use,183,184there is little
evidence on which to base estimations of future gains. Specifically, there is little evidence on how far attitudes to or experience of public transport in adolescence might translate into adult behaviour. Robust cohort studies are needed that track changes in behaviour (and ideally, as above, health outcomes), particularly for young people, over time. Transport interventions (e.g. the introduction of hire bikes) or workplace or school health promotion programmes would provide an ideal setting from which to recruit cohorts to explore the effects of changing travel patterns on health.
Transport as social practice
This raises a more general question about the cultural meaning of different transport modes, and how these change. It has been suggested that a key element of reducing car dependence will be to improve perceptions of public transport such that it is no longer seen as low status compared with car travel.111,182
A small social science literature now addresses the ways in which transport mode choices can be interpreted as social practice, in that they reflect not just individual decisions (based on, say, barriers and facilitators), but are embedded in cultural and materialfields.185–187There has been less research on how
these change. In this study, we suggested that the‘normalisation’ of bus travel has changed the meaning this mode has in London. We also suggested that‘cycling’ continues to be invisible to most young people as a candidate mode of transport. Research from sociology or anthropology that addressed‘bus travel’ or ‘cycling’ as social practice, and how their meanings change in relation to changing environments and policies, would generate useful information for informing interventions and promotional materials for those interested in increasing the modal share for either‘active’ or public transport. One particularly urgent need is for research on driving as social practice, to understand better the role of driving for young adults, and to explore the noted declines in driving and car ownership in some groups of young adults. This would provide invaluable base line information for future evaluations of schemes such as graduated driving licences.
Road traffic injury rates for young adults
This study was not powered to look specifically at the impact of change in travel modes on RTIs in young adults. Any future evaluation of the impact of reduced driving rates in young adults could usefully address the question of whether or not mode change (e.g. from car travel to public transport) is associated with reduced injury rates for young adults. The proposed introduction of Graduated Drivers’ Licenses in Northern Ireland would be a timely opportunity to address this.
Value of a statistical life for young people
The need for further research on the health impacts of active transport for young people raises the issue of whether or not monetary values that have been determined based on an adult population could be applied without change to the age group (12–17 years) in this study to determine the monetary benefits from changes to levels of physical activity, assaults and casualties. Although there has been a growing body of research that focus on this issue (see WHO130and Leung and Guria188), indicating that differing
values should be applied to children, Alberini and colleagues189conclude‘that there is no single ratio
which can capture differences in risk preferences for children and adults, [but] there is some evidence that the VSL [value of statistical life] for a child is greater than that of an adult’.
Theoretically, an individual’s own VOSL is driven by life expectancy – decreasing with age – tempered to some extent by the level of risk– which increases with age.190Other factors are however important. First,
young people’s health and safety is valued not only by themselves but by their family and friends, and
Blomquist and colleagues,192Hammitt and Hanninger193). Second, in policy evaluation, there is a tradition
of equal treatment, using social values based on political and ethical judgements, not only individual or familial VOSL. Thus, for example, the values used for road casualties in transport CBA are set equal for all ages,126and values of travel time are set equal across regions with very different household income and
ability to pay.194,195So, for example, if we were to propose differentiated VOSL for children and adults
(higher for children) based on an individual or familial valuation, we would need to consider the
implications for other groups (older people or adults in middle age) for whom individual/familial VOSL may be lower than the mean.
Further research is needed to definitively show how these differences in risk preferences translate into changes in values. In this study we have applied the adult values to the 12- to 17-year-old age group; hence, based on the available research on adult compared with child values the benefits are conservatively estimated.