We made two versions of the questionnaire to limit size and cognitive burden to the respondents; one version is focusing on road traffic-related air pollution and the other on road traffic related noise. Questionnaires on air pollution or noise were randomly assigned to respondents, i.e. respondents were provided with either
WTP questions on air pollution or noise. First questions on general WTP were followed by a series of questions on the health gain in specific effects of air pollution or noise related to a specific pollutant reduction. See Appendix B for the wording of these questions.