Karl T. Ulrich, a professor at the Wharton School of the University of Pennsylvania, has put forth a provocative theory. Traveling by bicycle, he argued in a recent paper, may cause more environmental harm than driving around in pollution-spewing, fossil-fuel-swallowing cars and sport utility vehicles.
How can this be? Bicyclists are healthier, he wrote, so they live longer. Over their lifetimes, they consume more energy than they save.