7.4.11.4 Methods – Project Level

For appraising different options, a more detailed assessment of the scheme benefits is generally justified. Walking and cycling schemes which increase physical activity can be expected to deliver two types of benefits:

• Reduced mortality rates; and
• Reduced absenteeism rates.

Both walking and cycling schemes are typically relatively small in nature. As such, it is important that the level of resources devoted to their appraisal is proportionate to the scale of the project or the likely impact of the project.

The methodology to be employed is that set out by the Department for Transport in WebTAG Unit 3.14.1, and is described below.

Estimating the impact on mortality

The methodology for calculating the former is taken from the World Health Organisation project Quantifying the health effects of cycling and walking (2007) and its accompanying model the Health Economic Assessment Tool for cycling (HEAT). Although this approach captures only the benefits associated with reduced mortality and not those associated with reduced morbidity, these impacts will to some degree be captured by the assessment of absenteeism rates.

The HEAT methodology involves calculating the number of preventable deaths per person taking up moderate physical exercise through walking or cycling. The modeller should make use of standard values for the prevention of a fatality, giving a value to the benefits of changes in mortality as a result. As with the evaluation of accident benefits over the appraisal period, the value of a life will increase in line with real GDP growth per capita (i.e. where people are becoming more economically productive), largely offsetting the discounting effect that applies to other costs and benefits. See the NESA Manual for these values.

The Copenhagen Centre for Prospective Population Studies found that individuals that cycle for three hours per week reduce their relative risk of all-cause mortality to 72% compared to those who do not commute by cycle (Andersen et al, 2000). For weekday trips, this accounts for 36 minutes per day. It is intuitive that the relative reduction in all-cause mortality of walking is different to that of cycling; a maximum achievable relative risk of 0.85 for walkers (at 36 minutes per day) is recommended. The modeller should assess the impact of a proposed scheme on journey distances and also on cycling speeds if it is considered that this will be affected significantly. From this, an average journey time may be estimated for new users. For more detailed information on the practical inference of changes to trip length at the local level resultant from a scheme, refer to Section 11.3.8 of the Design Manual for Roads and Bridges (DMRB).

From the average journey time, a relative risk of all-cause mortality specific to the average individual using the scheme may be calculated. This may be done by a linear interpolation between 0.72 and 1 for cycling, or 0.85 and 1 for walking, if the average travel time per day is less than 36 minutes, taking into consideration the proportion of users that make return trips along the route. Linear extrapolation can be used where average walking and cycling times are expected to be greater than 36 minutes per day. Where it is assumed that speed is not a specific consideration (being relatively constant from one area to the next), we may simply use the distance as in the example below. For the period of the appraisal, the health benefits must be calculated each year and then discounted in the usual way.

Table 7.5 - Cycling example

Note that if more accurate figures for mortality from physical inactivity are available from the locality concerned, these should be used but as local values may be highly variable there is a risk of bias. Any large deviations from the average should be noted and comparisons made with the average value.

The methodology above is based upon a range of assumptions which are discussed in more detail in WebTAG Unit 3.14.1; however, one important assumption is that of accrual, which is discussed below.

It is accepted that there is a period where the health benefits will accrue over time until an individual is deemed "fully active" and to derive the full health benefits of their trip-making activities by active modes. Further research is required to better define this accrual period. Therefore, making the benefits instantaneous to new users will be an-overestimate, which the practitioner may address through estimating the accrual period and applying this in the appraisal calculations. A five year accrual period is recommended. A linear interpolation between 0 and 100% can be used to distribute benefits across this period.

Transport Scotland recognizes that the appraisal of the health benefits associated with walking and cycling is an area of appraisal that is still immature and for which the evidence base is still growing. Transport Scotland will continue to monitor developments in this area to ensure that this guidance represents best-practice.

Estimating the impact on absenteeism

Reductions in short term absence from work can result from the improved levels of health of those who take up physical activity as a result of a walking or cycling intervention. These benefits can be monetised and entered into the appraisal as a value in the AST Table under the physical fitness heading though it should be noted that these are business benefits rather than consumer benefits. The method suggested here is that used in TfL (2004).

In the USA, physical activity programmes involving 30 minutes of exercise a day have been shown to reduce short-term sick leave by between 6% and 32% (WHO, 2003). In the UK and Scotland the average absence of employees is 6.8 days, of which 95% is accounted for by short-term sick leave (CBI, 2003). Therefore, for each employee who takes up physical exercise for 30 minutes a day for 5 days a week as a result of a walking or cycling intervention, the annual benefit to employers is likely to be (on average) at least 0.4 days gross salary costs (6% of 95% of 6.8 days).

In order to calculate the benefits, this figure needs to be combined with the average gross salary costs and the number of affected working people. Average gross salary cost figures may be found in Section 9.5.12. This can be combined with average hours worked per day to generate a gross salary figure. 2002 market price values should be used, for consistency with other elements of the appraisal. This value should also increase over time to reflect increased wages and productivity in line with real GDP per capita.

Table 7.6 - Example application to a walking scheme

Regional estimates of average hours worked per day may be obtained from the Census.

The number of working people affected may be calculated from the number of new walking and cycling commuters who are expected to use the facility. These benefits should not be subject to the 'rule of a half' which is consistent with the treatment of other benefits from improved levels of health and accident costs.

Practitioners should report the benefits associated with a reduction in short-term sick leave of 6% as a scheme's core benefits. The level of benefits associated with a reduction of short-term sick leave of 32% may be reported as a sensitivity.