Free Floating Electric Car Sharing in Smart Cities: Data Driven System Dimensioning

Car sharing is a popular means of transport in smart cities. The free floating paradigm lets the customers autonomously pick and drop available cars freely, within city limits. In this work we study the different policies when designing an electric Free Floating Car Sharing (FFCS) system. This system has the need to guarantee battery charge, a time-consuming operation, for which charging stations availability becomes a key factor for the sustainability of the whole system. We harvest the data of an already operative FFCS provider, and extract information about actual users' driving patterns. We implement a trace driven simulator to replay collected users' trips and simulate car batteries consumption for different design parameters. In this work, we limit the study to a single city, Turin (Italy), where we leverage actual trips registered over 2 months. We analyse and discuss several system design alternatives: the number of charging stations, their placement, and when to force users to return cars for charge. We identify regimes where cars never discharge and users can freely drop cars anywhere, albeit they are rarely rerouted to a charging station, possibly located in a nearby area to their original destination. Surprisingly, our data shows that even few charging stations (15 or more, i.e., 6% of city areas) guarantees the system to work almost autonomously, making thus possible free floating car sharing a feasible solution with electric cars.