University of California Transportation Center

This is an empirical study of food shopping trips in Seattle, Washington. In travel forecasting models, land use activities and transportation systems are assumed to be in static equilibrium. This paper deals with the dynamic nature of urban systems, specifically the interaction between food retail distribution systems and transportation systems. The research questions were: how long does it take these systems to reach an equilibrium and to what extent do transportation systems respond to location choice of food stores? In this paper, we examined changes in travel distances to and from food stores with respect to the location of food stores. In theory, if stores are optimally located with respect to the market area served, then store size and market size should be in equilibrium. To observe the equilibrating character of retail and transportation systems, actual store location patterns were compared with optimal store location patterns at several points in time using travel distance measures. The study showed that transportation systems and food retail distribution systems adjusted to each other and the process of adjustment took several decades to reach an equilibrium. During the past 50 years, store size and travel distance converged at only one point in time, around 1985. The findings of the study suggest that dynamic-equilibrium based models would provide a better predictive capability for long-term projections than static-equilibrium based models.