We recently sold our second car and only kept the fun but very impractical Mazda Miata. So I signed up for Zipcar for when we need a larger car. We have three Zipcars parked in our building's parking lot. In our case, the math was even more compelling. Between parking, insurance, registration, depreciation, and maintenance, selling the car is going to save us nearly $7K per year. We live in downtown San Francisco. We don't drive much at all, except on the weekends when we go out of town. We should have sold the second car 3 years ago, when we moved here. But we have always had 2 cars and we were reluctant to give up that second vehicle (burb mentality). People's reaction to our decision to sell the car has been one of disbelief. And when we add that we also cut Cable TV, then they really think we are off our rockers. So we must be on the right track.
If we did not go out of town so often (nearly every weekend), I would sell the Miata as well. With the subway, Zipcars, taxi cabs, Uber, Lyft, etc... there is no shortage of in-town transportation choices to get around.
By the way, gas and insurance is included when renting a Zipcar.