Polluted air means city walkers and cyclists should watch their speed

Bigazzi: The findings show that there is an optimal speed which leads to the least total pollution inhalation dose over a trip – what I call the minimum dose speed (MDS). The MDS depends on a number of personal, bicycle, and roadway factors, such as body mass and road grade. Across a wide range of people, the MDS is 3-6 km/hr walking and 12-20 km/hr bicycling on level ground. The MDS is lower when going up hills. For the vast majority of people, the MDS corresponds to a moderate exercise intensity on relatively flat terrain. Moderate exercise intensity can be roughly judged as being too winded to sing, but not so winded you can’t hold a conversation. The good news is that moderate exercise intensity is associated with the positive health benefits we expect from exercise.

RG: How do these speeds compare to how fast most people cycle and walk?

Bigazzi: The minimum-dose speeds are similar to what we see in on-road studies of people walking and biking. So people are already traveling around their optimal speeds from an air pollution point of view, which is good news. I don’t imagine this is because they’re trying to minimize their inhaled dose, and speed choice behaviour is something I’m in the process of researching.