The WSB intervention was not effective or cost-effective in terms of its effect on obesity in children under the current assumptions. The ICERS, even with cost-offsets included, were very large. The reasons for the intervention's poor performance in terms of its cost-effectiveness are several. Firstly, it was modelled on the basis of the relatively low recruitment and uptake of the program in Victoria as at 2004.
It could be reasonably argued that the program has not yet reached steady state. There appears to be considerable unutilised capacity within the current delivery model, and consequent scope for expansion of the program within the current infrastructure arrangements. The number of participating local governments and schools, the number of WSBs per school, and children per bus, could all potentially be increased without expansion of the infrastructure capacity at either the national, state, local government or school level. Sensitivity testing showed that improvements on a number of fronts are required to bring the intervention into the realm of cost-effectiveness as an obesity reduction measure. However, whilst cost-effectiveness could be improved by a more comprehensive coverage and uptake of the program, the number of children required to participate at these levels may not be realistic in the Australian context.
The WSB was not designed as an obesity prevention initiative, despite often being marketed as such http://www.vichealth.vic.gov.au/Programs-and-Projects/Physical-Activity/Active-and-Safe-Travel-to-School/Walking-School-Bus.aspx. The program was intended to produce change in the active transport behaviour of students. It has a number of objectives, all of which may result in potential positive side-effects (such as a safer traffic environment around schools, reduced congestion, accidents and pollution), provided that the intervention is shown to be effective in increasing the number of children new to active transport. Whilst these other benefits were documented in the second stage filter analysis, they were not incorporated into the technical results. It could be argued that the costs associated with the intervention should not have been fully attributed to the BMI outcomes, but be apportioned across a range of program objectives as was done under Scenario 2 of the sensitivity analysis. Given our adoption of a societal perspective, the choice was to capture all benefits and all costs, or alternatively, to capture only benefits and costs relevant to our objective. The latter path was chosen as data were lacking on broader benefits enabling their quantification. Whilst this evaluation concluded that the WSB was not a cost-effective intervention for obesity, its merits and potential benefits in terms of a range of other outcomes are acknowledged . However, given the high cost of the intervention in terms of each child new to walking to school ($2,900) under the base case assumptions, the other benefits would need to be substantial.
Incorporation of the multiple benefits of the program within the technical analysis was neither appropriate nor possible within the context of the ACE-Obesity study. The ACE methodology is premised on the application of consistent evaluation methods to all of the interventions, and the use of the same outcome measures (in this case, BMI and DALYs saved). Cost-effectiveness and cost-utility analyses were employed to facilitate comparison with the other interventions where the same outcomes were measured. The other benefits are, firstly, not relevant to the focus of the current study, and secondly, no measurement has been undertaken within the WSB program to show that such perceived benefits have actually been realised by the program. An economic evaluation of the WSB program as a stand-alone intervention taking into account all its potential benefits would necessitate new empirical data collection around a range of outcomes, and the potential use of different evaluation methodologies (such as cost-benefit analysis where a monetary value is attached to both costs and benefits).
It may be possible to justify programs which have low direct effects such as WSB and changing school canteens  as 'lighthouse' interventions - meaning that they are visible demonstrations of appropriate actions that 'show the way' for broader actions and eventually changes in norms. Indeed, it is difficult to envisage a broad community effort to promote active transport without a program on school travel and healthy eating for children without school canteen changes. The counter argument to this 'lighthouse' approach is that it fosters a disregard for the importance of applying guidelines of efficiency and effectiveness in decision-making. Acceptance of the 'lighthouse' argument would need to be context specific with strong safeguards built-in around ongoing monitoring and evaluation to achieve 'value-for-money'. Our analysis suggests that more cost-effective programs to promote active transport are required and need to be evaluated. This could be achieved through improvements to the WSB or by different programs given the high cost of the WSB program as it is now.
Lack of data on the incremental change in the numbers taking up active transport as a consequence of the intervention was a key limitation of the evaluation. The limited evidence of effectiveness made the strength of evidence a key decision point. Data used in the modelling of this intervention was drawn from a one week snapshot of the VicHealth program . Only 26 of the 33 participating local governments submitted data, and program activity levels may be under-estimated. However, there are no data showing an increase in the number of children walking due to the WSB intervention. Other important decision points relate to the program's feasibility and sustainability without ongoing funding (Table 5). The information gaps identified highlight the need for better evaluations of public health interventions. Whilst modelling as a tool allowed decisions to be based on the best available data, the results for this intervention are not as robust as they would be if a stronger study designs (such as RCTs) had been used and actual outcomes (i.e. BMI) were measured.
The intervention offers some potential wider positive benefits which were not taken into account. For example, the inclusion of taggers (generally older children, who were not formally enrolled in the WSB program, but "tagged" behind the buses), would increase the number of children participating in the intervention on a national basis from 15,680 to around 19,300. For the taggers, a mean reduction of 0.019 BMI units for boys and 0.021 for girls was calculated and applied. This would enhance the intervention's cost-effectiveness as it would increase the total loss in BMI, without any additional associated costs. However, it should be noted there were no data to verify that these children were new to active transport following the introduction of the WSB program. Further work is required to establish whether there is an increase in the number of children walking and in the time spent in walking and whether the other possible benefits of the program are realised.
Furthermore, this still may constitute a conservative estimate of the benefit, as the intervention involves some whole-of-school activities which may have positive spin-offs to both the wider student population as well as to parents and the wider community. Wider reach and lower costs would improve the WSB credentials as a priority for funding. The central importance of school travel in the quest to increase active transport suggests that improvements in the WSB or its variants need to be developed and fully evaluated.