From trend spotting to trend 'splaining: Understanding modal preference shifts in the San Francisco Bay Area

This study examines changes in observable patterns of travel mode choice behavior over time, and attempts to explain these changes in terms of possible shifts in latent modal preferences, while controlling for the confounding influence of concurrent changes in the socioeconomic environment and transportation infrastructure. Using repeated cross-sectional travel diary data collected from individuals residing in the San Francisco Bay Area in 2000 and 2012, we develop a latent class choice model of travel mode choice behavior. Estimation results reveal ten segments across the pooled sample populations that differ from one another in terms of their demographic composition, the travel modes that they consider, and the relative importance that they attach to different level-of-service attributes, namely travel times and costs. Findings indicate shifts in latent modal preferences that exceed analogous changes in observable travel mode choice patterns. For example, private (motorized) vehicle mode shares decreased from 85.0% in 2000 to 81.2% in 2012, but the proportion of the population that only considers private vehicle when deciding how to travel is found to decline from 41.7% to 23.5% during the same period. Changes in economic and social factors and changes in the level of service of different travel modes are found to have had a marginal effect. Had modal preferences not changed between 2000 and 2012, over and above changes in the socioeconomic environment and the transportation infrastructure, our framework predicts that private vehicle mode shares would have increased to 88.3% by 2012. Finally, shifts in modal preferences are not found to be limited to any one generation but to have cut across the entire population, reflecting broader cultural shifts that have transcended generational differences. (C) 2016 Elsevier Ltd. All rights reserved.