Abstract
Cycling is a popular means of transport in cities, this experimental wind tunnel study models groups of cyclists' exposure to road vehicle emissions on a typical London street. Transport for London state that polluting vehicles are responsible for half of London's air pollution and research shows a direct link between poor air quality and increased rates of respiratory diseases. Cyclists are particularly at risk due to their increased inhalation rates and proximity to traffic, therefore expressing the importance and significance of this research. This is the first study to specifically look at the implications of cycling in groups, often the case in congested cycle lanes at peak hours. The results of this project, carried out in the Environmental Flow wind tunnel, confirm that pollutant concentration decreases rapidly with increased separation distance from an exhaust when a rider and vehicle are in line. However, cyclists at the front of a group of in-line riders are subjected to the least pollution when adjacent to polluting vehicles, regardless of their separation distance. Following other riders may therefore increase exposure to air pollution. The increased pollutant concentration observed in groups of riders is likely linked with the complex aerodynamic field generated by upstream cyclists, trapping the vehicle exhaust fumes among the riders. This is combined with the reduced wind speed within groups which is less effective at sweeping the pollutants away. These findings suggest policy makers should construct wider cycle paths, or even better, separate riders from the road. Meanwhile, cyclists should distance themselves from both vehicles and other riders to minimise exhaust emission exposure. Drivers should also be advised to maximise the space they leave cyclists on the road.