Abstract:Using six-week travel diary data from Karlsruhe and Halle, Germany, this study examines the characteristics of individuals' action space. The extension of action space is represented by the second moment of the activity locations it contains, and day-to-day variation in the second moment is examined. The results show that out-of-home activity orientation and commitment (e.g., obligatory activities on weekdays and discretionary activities on weekend days) influence the extension of action space. For workers and students on weekdays, the spread of activity locations and the distance from home to the centroid of activity locations are relatively stable from day to day. It is shown that a substantial portion of the variations in their action spaces is due to unexplained differences across individuals that remain stable over time for each individual (unobserved heterogeneity). On the other hand, random factors have dominant influences on non-workers' weekday action spaces and all individuals' weekend action spaces.