I bicycle commute to work twice a week out of five days-- the rest I drive. I could commute four days a week, but there are varied reasons I only commute two. When I decided to take this on, I purchased a Trek 520 touring bike to use for both purposes, as well as Ortlieb panniers, Brooks saddle, an extra light, mountain bike pedals and shoes and a cycling rain jacket and pants. I'm married, so I felt the need to justify all of these purchases to my wife. So prior to making the purchases, I figured out how much I would save on gas, oil changes, wear and tear of the car and the projected extension of the life of the car. With all of my new bicycle purchases, I figured out that those purchases would pay for themselves within two years if I commuted three times a week or about three years if I commuted twice a week. I even factored in the cost of new bike tires and other maintenance bike parts. I've been doing it now for almost five years, and I'm so glad I do it.