At $3.00 per gallon, I "save" $1.50 in gas per day of commuting. BUT, the teenage kid wants the car available, so I would be "unable" to drive to work even if I wanted to. Therefore, my choices for getting to work (walking is too far) are to ride or to spend $4.00 on the bus. Therefore, I actually "save" $4.00 a day by biking.