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Impact of COnstructing Non-motorised Networks and Evaluating Changes in Travel
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Home | background | 3. Limitations of existing research evidence
3. Limitations of existing research evidence

background

3. Limitations of existing research evidence

Why important?

Although current policy documents often advocate altering transport infrastructure to make conditions for pedestrians and cyclists more attractive, there is little evidence from robust studies to show that doing so leads to an increase in walking or cycling, let alone changes in overall physical activity or carbon emissions (National Institute for Health and Clinical Excellence (NICE), 2008). This lack of evidence reflects a number of unresolved challenges in this area of research, particularly those of measurement and evaluation. The difficulties of measuring and assessing trends in walking, cycling, and physical activity in general are illustrated by the observations that National Travel Survey data suggest a decrease in distance cycled in the first half of this decade whereas traffic counts suggest an increase (DfT, 2005) and that it has been impossible to establish from Health Survey for England data whether the trend in overall physical activity is rising, falling or static (Stamatakis et al., 2007). Accurate measurement of walking and cycling using self-report instruments is notoriously difficult: short trips tend to be under-recorded in travel surveys, some groups associated with high levels of cycling (e.g. young men and students) tend to have low response rates to surveys, and many traditional physical activity questionnaires are designed to ascertain leisure activities rather than walking or cycling as modes of transport. The EPSRC funded CAPABLE project shows that self report instruments are particularly problematic for children (Mackett et al., 2007).

The lack of credible evidence of the effects of infrastructural interventions on population levels of walking and cycling partly reflects these measurement problems, but also reflects the difficulties of applying robust evaluative study designs to interventions of this kind: most previous studies in this field have significant methodological limitations such as a lack of representative population samples, a lack of prospectively-collected data, a lack of control groups or areas, or a short duration of follow-up (NICE, 2008), and only limited inferences about population impact can be drawn from current routine user monitoring data such as those collected by Sustrans on the National Cycle Network (Cope et al., 2003). As a result, regional and local government, health authorities and other public bodies lack the means to assess the potential travel, physical activity and carbon impacts of different approaches to promoting walking and cycling, to set appropriate targets, or to allocate resources appropriately.

Links

  • NICE (2008)
  • DfT (2005)
  • Stamatakis et al. (2007)
  • Mackett et al. (2007)
  • Cope et al. (2003)

site by Christian Brand, ECI