Here’s the case.
Derek Dunn-Rankin, a professor of engineering at the University of California, Irvine and an avid environmentalist, computes that a 180-pound person walking one mile to and from work at a pace of two miles per hour will burn 200 calories above the 2,000 calories burned each day to maintain the body’s basic metabolism. However, the production of those 200 calories in food takes fifteen to twenty times as much energy in the form of fossil fuels. This means that driving a high fuel economy car (40 miles per gallon) will use, in fossil fuel energy, only about two-thirds to one half the energy that the person uses in replacing the calories expended on walks. (Heavier walkers use even more energy when they walk and when they replace the greater calories they expend in moving their weight.) Energy use and pollution do not have a one-to-one correspondence, which causes Dunn-Rankin to conclude, “My bottom line would be that walking can be 1.5 to 2 times more polluting than driving (if you use a high mileage car). If you use a monster car, you are better off walking always.”16
The full post, by Richard McKenzie, is here.