DOE OSTI2017
Throughout the 20th century, automobiles have shaped urban and suburban landscapes, especially in North America. Globally, the car-centric transportation paradigm has contributed to unprecedented issues in terms of air quality, fossil-fuel dependence, carbon emissions lock-in, traffic congestion, road safety, parking scarcity, serious public health concerns, and socioeconomic inequality. Nonetheless, in the United States the percentage of single-occupant vehicle (SOV) commuters has continued to rise since 1960 while the proportion of carpooling has decreased by more than half since 1980. Evolving mobility services, in conjunction with new behavioral insights, have motivated recent inquiries in how to best foster sustainable growth while reducing traffic congestion and improving health outcomes. Few studies have assessed their true effectiveness, unanticipated effects (e.g., 'dead-head' or 'empty-vehicle' ride-hailing trips) or measured their impact on a specific city (e.g., modal shift, changes in personal miles traveled/vehicle miles traveled). This effort aims to answer the following questions: to what extent can shared mobility help invert the trend of increasing SOV trips? What are the energy risks and benefits of shared mobility? How do interactions between technology, policy, urban design, and behavioral change shape the transition to energy-efficient transportation? To this end, an assessment framework for sustainable urban mobility is developed, incorporating behavioral metrics (percent active transportation, percent transit ridership, percent shared trips), energy use (vehicle miles traveled per capita, percent SOV trips) and urban planning (population density, average commute time). We apply this framework to three cities (Denver, CO; San Francisco, CA; and Paris, France) to evaluate the sustainability of their transportation systems and explore their potential for shared mobility. The influence of incentives, social norms, and public perceptions on the uptake of energy-efficient mobility is further investigated through a review of current policy initiatives and identified best practices. The results from these three cities show strikingly different profiles: SOV trips range from 70% in Denver to 30% in San Francisco and 17% in Paris while transit ridership is 7%, 25%, and 64% of trips, respectively. These figures seem to correlate strongly with population density and degree of mixed-use development, with a ten-fold increase in density from Denver to Paris. Factors such as urban governance structures and level of public transit service further help to explain the observed differences. The framework presented here will help understand the long-term impacts of novel shared mobility solutions to better inform future policy making and investments.