They aren't the most efficient mode of transportation, depending on your definition. In terms of carbon, energy utilized, or even time, in many places walking/biking will beat cars. It's not a moronic conspiracy theory to suggest that bringing a 2 ton wheel-chair everywhere we go is inefficient.
In very few places in America is walking/biking more efficient than cars. The author is not saying autos are inefficient, which is a valid argument, he is saying there is a conspiracy ("automobile supremacy") to supplant other forms of transportation with the automobile. This is simply foolish.
