Generally shared cars only make sense when someone drives very little anyway. Cars are expensive and so shared cars are either too expensive to be used often, or very hard to get at. Renting a car for a weekend is about half the cost of a monthly payment on the same car, but if you buy the car you have it the rest of the month (and if you buy a car you have used options or keeping the car after it is paid for to bring the total cost down - you will have to pay maintenance costs but those tend to be much less).