Our study investigated in five European countries the willingness to-pay (WTP) to avoid the health effects associated with traffic-related air pollution and noise. This was done simultaneously for both pollutants using a single instrument: an open-ended web-based questionnaire. The general objectives were to assess and compare the monetary values of air pollution and noise health risks based on stated WTP by the respondents. Specific research questions addressed the
respondent's WTP to avoid the health risks from road-traffic related air pollution and noise, the determinants associated with the WTP for these health risks, and the differences in WTP values across countries. There were approximately 5000 respondents participating in each pollutant sections in the questionnaire, making our study larger than most other monetization studies of environmental health effects.