The study found that cycling even for a short period of time in traffic can lead to significant exposure to components of car exhaust, such as tiny particles and soot, that may contribute to respiratory and heart problems. Because cyclists tend to breathe about twice as deeply as car drivers, they inhale larger amounts of air pollutants.

The researchers also calculated the risk of dying in a traffic accident as about four times greater per half-mile traveled for cyclists than for car drivers.

But they determined that the health benefits for cyclists in The Netherlands were at least nine times greater than the hazards. By switching from driving to cycling, people would, on average, live three to 14 months longer because of increased physical activity. The risks they would face would be potentially losing 0.8 to 40 days of life because of increased exposure to air pollution and an average of five to nine days from a fatal traffic accident.

The findings were reported online June 30 in Environmental Health Perspectives.

Switching to cycling was also found to benefit public health because it would eliminate 500,000 car trips a day, leading to a reduction in air pollution, the researchers noted in a news release from the publisher.