I don’t mean to discourage anyone from riding a bike to work, but this is worth keeping in mind:
Let’s assume you saved a gallon of oil in your commute (a generous assumption!). Global daily energy consumption is 9.5 billion gallons of oil equivalent. … So by biking to work, you save the equivalent of one drop in 10 gasoline tanker trucks. Put another way, it’s one pinch of salt in a 100-pound bag of potato chips.
This is from John Stossel’s recent article in the Reason magazine. Read the whole thing.