Conditions of transportation were investigated as sources of psychological stress as they affect the physiology, task performance, and mood of commuters. Participants in the study were 100 employees of industrial firms. Traffic congestion was construed as a behavioral constraint in terms of the concept of impedance which is defined by the parameters of distance and time. It was expected that the effects of impedance would be mediated by personality factors, such as locus of control. Multivariate tests of the internal validity of the impedance factor were significant. However, significant main effects for impedance were obtained only for mood and residential adaptation. The predicted interactions of impedance with locus of control were obtained across task performance indices. In multiple regression analyses, the distance and speed of the commute to work were found to account for significant proportions of variation in blood pressure, while several indices of personal control had significant regression effects on the task measures. The implications of the results for research in community psychology are discussed.