One of my goals in life is to get more people riding their bikes. This is easier said then done. Bike commuting is hard, but not for the reasons you probably think. Yes, there is a fitness aspect to it but that can be easily overcome--more on this below. But the mental (i.e. logistical) hurdles are more difficult to surmount.
Any time you use your bike when you otherwise would use your car. The end goal is replacing what otherwise would have been car mileage with bike mileage.