Abstract:Stability in travel over time is examined in this study, and the source of observed instability is decomposed into: change in socio-demographic and other contributing factors, and change in structural relationships underlying travel. As a tool for this analysis, simultaneous equations model systems are developed to describe urban residents' activity-travel patterns. The models are estimated using repeated cross-sectional data from the Kyoto-Osaka-Kobe metropolitan area of Japan, collected in 1980, 1990 and 2000. The results of statistical analysis indicate that the structural relationships are instable, that changes in non-workers' travel patterns are largely due to the instability in the structural relations while changes in demographic and socio-economic factors play relatively minor roles, and that urban residents' travel has the tendency to expand over time.