Commuter Cycling: Exposure vs Dose (Why Stoplights Matter)

Your actual pollutant intake depends on three variables, each of which you can influence to some degree:

Concentration is what’s in the air around you. Ventilation rate is how much air you process per minute. Duration is how long you’re exposed. Reducing any one of these three factors lowers your total inhaled dose.

How much air you process depends on your activity intensity:

Higher ventilation rate means more air processed per minute — and more pollutants drawn into your lungs. This is why intensity matters, not just duration.

Despite being in traffic for less time on most commutes, cyclists often process significantly more air per minute than car occupants (commonly around 2–4x, depending on intensity). Over a typical commute, this means more total air — and potentially more pollutants — pass through a cyclist’s lungs.

However, the picture is more nuanced than it first appears. Car cabins are not sealed environments. In-car concentrations can be similar to or even higher than on-bike concentrations, depending on ventilation settings, whether windows are open, and position in traffic. Cyclists also tend to ride at the edge of traffic, while drivers sit in the middle of the exhaust cloud during congestion.

Intersections with traffic lights are where vehicles idle and then accelerate, producing peak particle and NO₂ concentrations. Cyclists waiting at a red light are stopped in the middle of this pollution cloud — at high breathing rates if they’ve just been pedaling.

The combination of high ambient concentration and elevated breathing rate at stoplights creates a disproportionate share of your total commute dose, even though you may only spend a few minutes at red lights.

Side streets and separated cycle paths can have substantially lower concentrations than main roads. A route one block off the main arterial may add a couple of minutes to your commute but reduce your pollution exposure by 30–50%.

Slightly longer but lower-intensity routes also help. If a quieter route lets you ride at a more moderate pace, your breathing rate drops too — reducing dose from both the concentration and ventilation sides of the equation.

E-bikes can reduce dose further by lowering the rider’s exertion level. With pedal assist, you breathe less heavily for the same speed, directly lowering the ventilation-rate component of your inhaled dose.

Multiple large-scale studies — including de Hartog et al. (2010), Tainio et al. (2016), and Cepeda et al. (2017) — consistently find that the cardiovascular and mortality benefits of cycling far exceed the health costs of pollution exposure, by a wide margin.

This holds true even in moderately polluted cities. The goal is not to avoid cycling, but to minimize exposure through smart route choices and timing. For most people, regular cycling remains a net health gain — even in imperfect air.