The case for cycling
People of average fitness can achieve 20 km/h with an average power input of about 1/10 hp, or 75 watts. This level of exertion is minimal and can be kept up for hours.
Leg muscles are about 20 percent efficient, so a five kilometre ride consumes 80 kilocalories, or about one small apple. If you are wondering, this translates into a fuel efficiency of 595 km/l (1,400 mpg) of gasoline. Apples are renewable and clean; gasoline is neither.