It is pretty easy to notice how many cars are traveling with a single occupant. There are a lot of empty seat miles going to waste every day. If four people ride in one car as opposed to four cars, the gasoline used will be almost one quarter. Especially for fixed routes that you take all the time and know ahead of time (like commuting to and from work) there are almost no negatives. It is great to have a car for unplanned trips and to give you the freedom to go where and when you want. But for the commute to work, most of us have no freedom anyway. You have to leave at a certain time to arrive at a fixed place on their clock, not yours. So carpooling to and from work leaves you with pretty much the same degree of freedom but costs only a fraction of the gas!