A quasi-experimental study was conducted to assess the effects of routine exposure to traffic congestion on the mood, physiology, and task performance of automobile commuters. Traffic congestion was conceptualized as an environmental stressor which impedes one's movement between two or more points. Industrial employees were assigned to low, medium, or high impedance groups on the basis of the distance and duration of their commute and were classified as either Type A or Type B on a measure of coronary prone behavior. As expected, subjective reports of traffic congestion and annoyance were greater among high and medium impedance commuters than among low impedance individuals. Also, commuting distance, commuting time, travel speed, and number of months on route were significantly correlated with systolic and diastolic blood pressure. Contrary to prediction, medium impedance As and high impedance Bs exhibited the highest levels of systolic blood pressure and the lowest levels of frustration tolerance among all experimental groups. The results were discussed in terms of the degree of congruity between commuters' expectancies and experiences of travel constraints.

Conditions of transportation were investigated as sources of psychological stress as they affect the physiology, task performance, and mood stress 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 only obtained 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.