Carpooling to work can save a huge amount of green, especially if you are commuting quite a distance. By sharing the cost of gas or participating in a ride share program you not only are saving yourself money on gas, but your car is being used longer and will have less wear on it which will hopefully mean there will be less maintenance and less oil changes and other routine maintenance to pay. In the process of saving all this green you are also limiting your contribution to carbon emissions released.
But think beyond just carpooling to work, what about when you & a friend are going out, or you are going to the zoo for a playdate. Be open to the possibility that there are many other times when carpooling might present itself.