In large cities, car sharing (example: Zipcar) can be convenient and financially beneficial to the user, but is it necessarily more environmentally sustainable?
More sustainable than what?
The car sharing option must be compared to what the user would otherwise use for transportation. If the user would normally walk, bike, and ride mass transit, then switching to car sharing would be a less sustainable practice. However, if the user would normally drive their own car for transportation, then the choice to ditch car ownership in exchange for walking, biking, and riding mass transit would seem more feasible if they had the option of car-sharing.
So car sharing enables a sustainable transportation lifestyle by providing a convenient and economical option for using a car when needed. Additionally, without the temptation of a car in the garage, the user would more likely consider sustainable transit options for each trip.
Resource inputs to car manufacturing
An additional, environmental benefit to car sharing is the decrease in demand for cars. With fewer cars being produced, fewer resources are being consumed and the environmental impacts throughout the supply chain of auto manufacturing are decreased.