Optimal cycling and walking speed for minimum absorption of traffic emissions in the lungs.

This study investigated whether, over a number of fixed distances and under a number of different exposure concentrations, the cyclist will adsorb less benzene by cycling/walking slowly with a relatively low breathing rate or by cycling/walking as fast as reasonably possible with a relatively high breathing rate. Breathing rates were measured in the laboratory for various cycling/walking speeds over set distances. These breathing rates could then be entered into a numerical model of the human respiratory tract together with the journey times and pollutant concentrations to assess the total absorption of pollutants in the lungs. Results show that cycling and walking at a relatively fast speed and therefore breathing at a higher rate over a shorter duration of exposure results in lower total absorption of benzene than cycling/walking the same distance at a slower speed. The magnitude of this reduction (was more notable at lower concentrations than at high concentrations in the alveolar region of the lungs and was more notable for the pedestrian than cyclist. The cycling at a faster pace resulted in a 17% reduction in total absorption, while walking at a faster pace resulted in a 26% reduction compared to travelling at a slower pace in both cases.