CNG’s are three wheeled “baby taxis”- the same as tuk-tuks in Thailand – that run on Compressed Natural Gas, a fossil fuel substitute for gasoline or diesel. They are about the size of a golf cart and are considered to be a more environmentally clean alternative to those fuels. Although it produces greenhouse gases, it is much safer than other motor fuels. Natural gas is lighter than air, so it disperses quickly when leaked or spilled. Another huge benefit is that it costs five time less then petrol.
CNG has grown into one of the major fuel sources used in car engines in Iran, Pakistan, Bangladesh and India. The government of Punjab, Pakistan, the most populous province of that country, has mandated that all public-transport vehicles will use CNG by 2007. Today all of the auto rickshaws as well as personal vehicles in Bangladesh are being converted to CNG powered technology, the cost of which is in the range of $800-$1000. In Dhaka not a single auto rickshaw without CNG has been permitted since 2003.
Considering the amount of traffic, air pollution isn’t too bad in Dhaka. I’ve heard it has greatly improved in the last ten years. Maybe the west can learn something from Bangladesh ?