Matthew Blackett of Spacing writes:
Sometimes it takes a visual illustration to make the strongest argument.
The above image is 42 Brompton folding bikes placed in one parking spot. The image below is the amount of space needed for the same amount of people to take a car, bus, or bike.
UPDATE: Proper credit was not given to BoingBoing and Jam Design.
Matthew also shows a version of the photo Mike showed in his post Amount of Space Required to Transport People by Car, Bus, or Bicycle, without the Comic Sans explanations. Spacing