What could be a clean, inexpensive and efficient way of transportation?

Bicycles are a clean way of transportation because they only use the power of the human body to function, are generally cheaper than other methods of transportation if compared to cars for example, and can be conveniently stored or parked in great quantities in reduced spaces. On top of all these benefits using a bicycle for transportation will render very positive benefits for one's health, by burning calories along the way and providing cardiovascular exercise every time.