Cyclists face least exposure to traffic fumes-it’s official.

Guest Post: Woody Pattinson from the University of Canterbury.

It’s time for another myth to be busted. You know how it goes. “How can you cycle in the city knowing you are breathing in all those toxic traffic fumes?” Read on and be reassured. Of course we know that motor vehicles cause the pollution, but it is inside motor vehicles where the greatest concentration of pollutants can be found. The bulk of scientific literature on cyclists’ exposure to traffic fumes reports that cyclists are among the least exposed.

Additionally, results showed that at a distance of 7 metres from traffic, exposure dropped considerably. Along with the other obvious safety benefits, this provides another significant argument for shifting cycle lanes from directly alongside traffic flows to between parked cars and footpaths, or splitting footpaths into shared cycleways, or developing ‘green routes’ that are away from high traffic volumes. Campbell Live on TV3 showcased this research recently. You can have another look at it here.

The study has been considered by Christchurch City Council staff for their next transport plan and was cited by a recent Australian study. Even New Zealand’s Minister of Transport, Steven Joyce, has recognized the merits of the research because of its ability to “demonstrate clear potential to improve transport planning and policy”.

The full details of the study can be found within the original thesis or you can read on for a summary that includes the detailed findings.

Those sitting on a bus or in a car can face up to 2-4 times higher pollutant concentrations than cyclists and pedestrians. Cyclists receive the least exposure to carbon monoxide (CO), volatile organic compounds (VOCs), particulate matter (PM2.5 & PM1.0) and ultrafine particles (UFPs) – which are now thought to be the largest threat to human health of all air toxics, due to their ability to deposit deep within the lungs and penetrate the blood-brain barrier.
This may seem counter-intuitive, but the thinking is that although cyclists encounter higher peak concentrations, toxic fumes enter vehicle cabins in various ways, trapping poor air inside for long periods. Subsequently, average exposure along a typical journey tends to be much higher. Vehicles are also prone to heavy self-pollution. This is generally in the form of ingression via ventilation channels, open windows and other ‘leaks’ – notably carbon monoxide for petrol vehicles and nitrogen dioxide for diesel vehicles.
Some studies argue that because the minute ventilation (volume of air per minute – breathing rate) is higher for cyclists, that their actual intake is higher than other modes. This argument is somewhat flawed because respiration rates differ drastically, depending on minute-to-minute stress factors and an individual’s level of fitness. Within the literature where ventilation rates are considered, cyclists’ travel speed and commuters’ stress levels are often ignored or based on a limited range of study participants.
Research comparing different modes of commuting was recently completed in New Zealand, where extensive sampling was carried out in Auckland and Christchurch. The study found that on-road, in-traffic cyclists were, on average, up to 61% less exposed to CO and UFPs, but up to 26% more exposed to PM1.0-10. This is simply explained by the fact that the larger particle fractions tend to be dominated by background sources such as industry and home heating, rather than emissions from vehicles. Cyclists sit slightly outside of the exhaust slipstream and are afforded greater dispersion from meteorological influences, hence their exposure is more representative of ambient concentrations – yet slightly elevated by exhaust plume peaks.
Additionally, as a world-first, the study assessed micro-spatial variation in exposure, relative to distances away from the traffic stream. Results showed that at a distance of 7 m from traffic, exposure dropped by 30% (UFPs), 22% (CO) and 14% (PM2.5). At 19 m, concentrations decreased a further 17%, 13% and 8%, respectively. Hence, the value in moving cycle lanes away from motorized traffic.

This research is supported by multiple published journal articles from England, Ireland, the Netherlands and Australia.

Any correspondence regarding this research can be directed to the author.

cycling/freedom