We all know walking and cycling improves air quality by removing motor vehicles from the road and replacing those trips with a mode that is emission-free. But what is the exact impact of walking and cycling on air quality? Is it measurable?
For the first time, we are able to reveal the extent of the exposure to air pollution on individuals, and the implications of poor air quality.
The current system
There is a fundamental flaw in the way that the air quality implications of transport schemes are assessed at present. When a scheme is evaluated, the ‘traditional’ approach simply assigns a value to units of dirty emissions.
Using transport appraisal mechanisms, we would estimate amounts of emissions from motor vehicles, and assign a standard ‘damage cost’ monetary value to them.
Notwithstanding the issue of motor manufacturers concealing the true volume of emissions, this is still a crude approximation of the real extent of the impact. The damage costs for pollutant, such as particular matter, PM10, and nitogen oxide, NOx, are standard values developed by Defra over many years.
They are useful for high-level policy appraisals where the key metric is an estimated reduction in the tonnage of a given pollutant. However, this approach conceals the extent of impact on people who move through the environments where these emissions happen.
A new approach
Sustrans wanted to move beyond assessing the value of potential ‘dirty emissions’ and be able to quantify their real-world impact. We wanted to be able to explore the direct, personal implications of dirty air on people, as a means of making a better case for investment in walking and cycling to help to address air quality.
Working with Eunomia we set out to model the implications of poor air quality on people.
We have built a model that uses data on the distribution of air pollution in the local environment and data on the extent of exposure through the duration of trips and respiratory rates, to generate outputs that quantify the extent of the personal exposure problem.
Calculating the impact of walking and cycling
The intention behind our model was to explore how much walking and cycling can help clean the air, thus providing an assessment of potential benefits. The results were very promising: the value of increasing active travel can be considerable, where certain criteria are fulfilled.
The model clearly shows us the value of increasing the number of people travelling by active modes (particularly when larger parts of that active travel are regular trips that have changed from more polluting alternatives), and of separating active travellers from the worst pollution hotspots, in addition to achieving reductions in emissions.
However, it also shows us that while the value of air pollution benefits that walking and cycling can help to realise are large, they are still only a small part of the overall net benefit associated with walking and cycling.
The gains would be even bigger if wider benefits of health from increased activity were included.
Wider policy context
Air pollution may become ‘more expensive’: for example, if the threatened fines for air quality incursions are levied; if the social distribution effect of poor air is properly reflected in values; or if businesses start to recognise the impact of poor air on their staff.
News of sophisticated air quality monitoring may be a step in the right direction - we are taking measurement of air pollution seriously, but still need solutions for dealing with it.
Walking and cycling have a huge role to play in addressing the challenges of air quality, and in ‘future-proofing’ against future costs. Plans to reduce polluting emissions from transport must include plans for effective investment in walking and cycling.