With the increasing human population, the number of cars hitting the roads have gone up. More cars generate more air pollution, increase traffic congestion and affect public health. In the US, for example, more than 80 per cent of the people commute by cars. Transportation by trains and others mass-transit systems are still to catch on in many parts of the globe. In developing countries like India, the number of cars is rising at an alarming rate. In these countries, only 5-10 per cent of the people can afford to buy an automobile, while up to 80 per cent can buy a bicycle.