This section examines the current evidence for the benefits of AST on: levels of PA; physical health-related outcomes; psychological, social and academic benefits; reducing the impact of motor vehicle usage.
1.5.1 Physical activity
A considerable number of studies indicate a positive association between AST and higher levels of PA (Faulkner et al., 2009; Schoeppe et al., 2012; Larouche et al., 2014), although the evidence is generally only of moderate quality (Larouche et al., 2014). For example, in a review of 68 studies (mainly cross-sectional), AST was associated with higher PA levels in 22 out of 28 studies involving accelerometry; the mean difference in time spent in daily MVPA ranged from 0 to 45 min (Larouche et al., 2014). In another systematic review of 12 higher quality studies (all reporting the use of objective measures), the weighted mean MVPA accumulated by walking to and from school was 17 minutes per day in primary school pupils (9 samples,
n=3422) and 13 minutes per day in high school pupils (4 samples, n=2600) (Martin et al., 2016). Pooled analysis suggested that walking to and from school contributed
Age 5-10 Age 11-16
North East 1.5 3.3
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23% and 36% of MVPA on schooldays in primary school age children and high school pupils, respectively.
Links between AST and PA may be moderated by gender, age, independent mobility status and distance, with boys (Davison et al., 2008; Faulkner et al., 2009), older children (Faulkner et al., 2009), more independent children (Schoeppe et al., 2012) and those living furthest away from school (Larouche et al., 2014) benefiting the most. Evidence for the role of other factors such as race and ethnicity in mediating the relationship between AST and PA was inconclusive (Faulkner et al., 2009). An important finding was that PA measured over the weekend consistently failed to reveal significant differences between school active and non-active travellers, suggesting that the higher levels of PA observed in active school travellers was limited to weekdays and therefore to the school journey (Davison et al., 2008; Faulkner et al., 2009; Larouche et al., 2014). It remains unclear whether AST promotion impacts on the formation of other PA habits (e.g. engagement in sports), possibly because there is currently weak evidence for the effectiveness of ATS interventions (Chillon et al., 2011), and how it affects PA in adulthood, mainly due to the lack of long-term prospective intervention studies (Larouche et al., 2014).
1.5.2 Physical health-related outcomes
Studies investigating the relationship between AST and health outcomes have mainly focused on fitness indicators, particularly weight status/body composition and
cardiorespiratory fitness. Body composition relates to “the relative amounts of muscle, fat, bone and other vital parts of the body” and cardiorespiratory fitness to “the ability of the circulatory and respiratory systems to supply fuel during sustained PA and to eliminate fatigue products after supplying fuel” (Caspersen et al., 1985). There is limited support for an association between AST and healthier body
composition (Sirard and Slater, 2008; Lubans et al., 2011a; Larouche et al., 2014) or BMI (Davison et al., 2008; Faulkner et al., 2009). One review found mixed (low quality) evidence for the role of AST on body composition, possibly due to
measurement inconsistencies between studies, confounding demographic variables, compensatory behaviours (e.g. reducing PA in other parts of the day), and analyses unadjusted for distance (Larouche et al., 2014). More clearly, there is consistent
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evidence that cycling to/from school is associated with greater cardiovascular fitness and that the mode of transport explains a substantial proportion of the variance in cardiovascular fitness (Larouche et al., 2014). Few studies have investigated correlations between muscular fitness or flexibility, providing equivocal evidence (Lubans et al., 2011a), and no study assessed muscular strength.
The distance to school, a strong predictor of AST, may help explain the weak link between AST and measurable health outcomes, particularly BMI (Faulkner et al., 2009), yet analyses do not always control for distance (Larouche et al., 2014). Active commuters tend to live closer to school and the distance they travel may be
insufficient to produce any noticeable changes in body weight. Many studies also fail to examine associations by sub-group, such as ethnic background or gender, which could reveal clearer associations between AST and health (Lubans et al., 2011a). Another limitation of studies investigating AST health outcomes is the range of definitions used to classify active travellers (Faulkner et al., 2009; Lubans et al., 2011a). Likewise, body composition relies on a range of measures including BMI, z- scores and percentiles, and parental proxy reports of their children’s height and weight (Lubans et al., 2011a). Thus, a more objective assessment of AST and physical effects is necessary.
Little is known about the possible long-term health benefits of walking or cycling to school compared to being driven although there are some indications of decreased risk of cardiovascular disease (Andersen et al., 2011). Smaller and population-wide health gains may also be achieved through reductions in air and noise pollution, but this is yet to be demonstrated in AST research (de Nazelle et al., 2011).
1.5.3 Psychological and academic outcomes
AST may have positive results at other levels, such as psychological, social and academic, but the evidence for this hypothesis is still scarce. In a cross-sectional study conducted in China (n=21,596, age 6-9), children who actively commuted to school showed lower odds of having depressive symptoms than those using passive transport to school (Sun et al., 2015). Another study (US) has found a positive
association between regular ATS and children’s perception of its health benefits (Merom et al., 2006). An increased interaction with other children is widely believed
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to be a key benefit of ATS (Rissel, 2009). Bus travel to and from school was
associated with higher self-reported bullying victimisation amongst Canadian male, but not female, students (n=5065, mean age 15.2±1.9 years) compared to ATS; however ATS females were more likely to report being bullied than public transport users during the journey to school (Sampasa-Kanyinga et al., 2015).
Two cross-sectional studies found an association between AST and
cognitive/academic performance. AST was positively associated with higher cognitive performance in adolescent girls (but not in boys), independent of a number of
potential confounders including extracurricular PA (n=1700; age 13 to 18.5 years); the association between AST and cognitive performance was stronger in those girls who travelled further to school (Martinez-Gomez et al., 2011). Similarly, Danish adolescents (n=10 380; age 13-15) who actively travelled to school perceived their school performance as higher than non-active travellers, even after adjusting data for potential confounders (Stock et al., 2012).
1.5.4 Motor vehicle use and air quality
Few studies have explored possible links between AST motor vehicle-related outcomes. One systematic review on active travel (not exclusively in the school context) found limited evidence for a shift towards less car use following school travel plans, with many studies lacking randomisation and a follow-up of adequate duration (Hosking et al., 2010). Another AST review found some evidence for a decrease in car use following ‘walking school buses’ and ‘walking promotion’ initiatives (NICE, 2007) while a more recent AST review did not report possible changes in motor vehicle before and after AST interventions (Chillon et al., 2011).
Efforts towards a decrease in motor vehicle usage, or at least a shift to more efficient modes (e.g. public transport), carry a potential positive impact at the environmental and social levels. In the case of AST, very few studies have attempted to account for such outcomes. An exception is a study in Canada where a reduction in CO₂
emissions were reported during a three year ‘Safe Routes 2 School’ campaign (NHTSA, 2004).
On the other hand, active travel policies alone are unlikely to bring about substantial improvements in air quality and noise and such effects may hardly be detectable by
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researchers (Krizek et al., 2009). In other cases, improvements in walkability through traffic calming can offset reductions in car use due to more stop-and-go traffic and congestion, increasing emissions per trip (de Nazelle et al., 2011). Children who shift to walking or cycling may also experience higher inhalation of air pollutants, noise and traffic hazards, but there is indication that the health benefits substantially outweigh the risks (Tainio et al., 2016).