Funny - my car (Toyota Prius) emits less carbon dioxide than if it's passengers would have been walking or running the same distance. This is the only such car.
A typical 70kg human burns about 75Kcal fat per km (running. Walking is even less efficient). That is about 1.05kg fat per 100km. Toyota Prius at slow cruise (80kph) burns about 3.3liters per 100km and can carry 5 passengers. Human fat has about the same energy density than octane (roughly 25% less).
It seems like lack of wheels is what makes our bodies so inefficient.
Speaking of which - many people attribute Prius efficiency to the hybridity - ability to regenerate energy back from breaking. They don't know that this is only one third of it's story. The #1 invention in the Prius is a unique continuously-variable transmission, of a type only possible in a hybrid car. The so-called ECVT, only possible in a hybrid car, is a complete wonder. It's a very lightweight transmission, which is truly continuous but does not have any ribbons or cones - all the way rigid toothwheels. How is that at all possible - is an amazing story. The third part is of course the Atkinson-cycle engine, which beats the inherent thermodynamic inefficiency of the 4-stroke ICE.