A regional survey methodology to estimate reductions in vehicle miles traveled and in emissions resulting from commute changes attributed to voluntary mobile source emission programs is described. This "switcher survey" determined the incidence of switches to alternative modes among commuters in the Atlanta metropolitan region and collected information about their travel before and after the changes were made. Researchers encountered many methodological issues relevant for other transportation demand management (TDM) evaluations, particularly those assessing emission reductions from regional TDM strategies. The survey methodology is described; issues addressed during the survey are discussed; and analysis implications of the issues are presented. The research was conducted, in part, to test the ability of the survey for this purpose. Several survey modifications are suggested to improve the survey and increase its flexibility for use in a variety of evaluation situations.