...Cars greener than people?

I recently read an article in scientific american that was quite interesting. Hybrid cars have become so eco-friendly they now trump at least one form of human locomotion. Alberto E. Minetti, professor of physiology at the University of Milan, along with his master’s student Gaspare Pavei, compared the CO₂ emissions of four men walking, running and biking with the emissions of a hybrid vehicle carrying those same four men. The scientists found that four men would release more CO₂ by jogging than if they boarded a hybrid car. (On average, four women jogging would release less CO₂ than if they rode in a car because of their lower body mass.) Maybe next time I will take a cab home instead of running?