September is my first full month of married life. Looking at our first month/budget vs. actual spending, I noticed our gasoline expenses were significantly below my target. Why? Carpooling saved me more money than I expected. How? Our Carpool works like this: 2-3 times per week, I hitch a ride to/from work with my wife (about 10 miles each way). She continues on to her job. We always take her Toyota Corolla (32mpg) for this.
Lets say we go 64 miles per week in a carpool. She uses 2 gallons of gas for a total cost of approximately $8. Had I been driving, I would have used about 3.5 gallons and spent about $14 for the priviledge.
Over the course of a month, we save $55-60 in after tax dollars. While I am in her car, her effective mpg goes from 32mpg to 64mpg.