The TRAVEL study examines exposure to air pollution of cyclists, car passengers and bus passengers. In addition, short term effects of these exposures are examined on lung function, air way resistance, exhaled nitrogen oxide levels and blood markers, among others markers of inflammation and coagulation. Volunteers were recruited through intranet websites of their employer. All volunteers were civil servants working in Arnhem, the Netherlands, employed by the local or regional government, or the regional public health service. The inclusion criteria, developed to study the health effects of commuters' exposure to air pollution, were being of age between 18 and 56 years and non-smoking. Exclusion criteria were suffering from chronic obstructive pulmonary disease or asthmatic symptoms, using asthma medication, and being exposed at work to fumes or dust, to avoid confounding of exposures other than the studied air pollution exposure.
The measurements of the TRAVEL study were done between June 2007 and June 2008. During the commute by bus, car and bicycle, the volunteers were wearing heart rate monitors. Each volunteer participated at most 12 times. Each volunteer travelled by all transport modes. The commuting trips had a duration of two hours, from approximately 8 am to 10 am. During the car rides the volunteers were passengers, the car was driven by one of the researchers. Heart rates were recorded using Polar RS400 heart rate monitors (Polar Electro, Kempele, Finland). Heart rates were recorded per second. On the first six days of in total 47 days heart rates were recorded each five seconds, erroneously. We checked all graphs of the heart rate during commuting for abnormal patterns. For further analyses we excluded the parts where the heart rate was 'incorrect', 'incorrect' defined as a heart rate remaining exactly constant for 30 time points or longer. In addition we excluded the complete trip if the heart rate data were missing or 'incorrect' for more than 20% of the total travel time.
The measurements of the TRAVEL study were done between June 2007 and June 2008. During the commute by bus, car and bicycle, the volunteers were wearing heart rate monitors. Each volunteer participated at most 12 times. Each volunteer travelled by all transport modes. The commuting trips had a duration of two hours, from approximately 8 am to 10 am. During the car rides the volunteers were passengers, the car was driven by one of the researchers. Heart rates were recorded using Polar RS400 heart rate monitors (Polar Electro, Kempele, Finland). Heart rates were recorded per second. On the first six days of in total 47 days heart rates were recorded each five seconds, erroneously. We checked all graphs of the heart rate during commuting for abnormal patterns. For further analyses we excluded the parts where the heart rate was 'incorrect', 'incorrect' defined as a heart rate remaining exactly constant for 30 time points or longer. In addition we excluded the complete trip if the heart rate data were missing or 'incorrect' for more than 20% of the total travel time.
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