Carpooling has been suggested as a solution to alleviate increasing gas prices. The problem is that finding someone to carpool with is a difficult task requiring much research into whether the driver is dependable, etc. Except for major cities it is even to time-consuming/costly to get a cab. Thus today it is highly convenient to own your own car.
A much better system would be if all car owners had an easy way of turning into part time cabbies. If people could expect a large fraction of drivers to be willing to take one for a ride at a price, this would significantly reduce the individual need for private cars. In general this would be a more efficient economic system as [unemployed] car owners would derive an income and car-non owners would save on car ownership.
It might surprise you to learn that such a system once existed. The semi-cabs were called jitneys (jitney=slang for nickel) where the expectation was that a ride cost a nickel. They were killed off by government subsidizing streetcars. Later the streetcars were bought out by the big automakers and the need for private car ownership was created.