Natural Gas Powered Vehicles

Why do some cabs have gas cylinders in the trunk?

Initially, I was disappointed to learn that they aren't due to some underground, Fast and Furious, nitrous-boosted taxi cab racing scene - where the stakes are high and the fares are even higher. The reality is much more pedestrian, but interesting nonetheless.

According to the numbers I've seen around the web, Colombia has between 200,000 and 250,000 vehicles that run on compressed natural gas (CNG). These vehicles are served by just over 300 CNG filling stations around the country.

Natural gas has several advantages over gasoline as a motor vehicle fuel. While still emitting the chief global warming culprit carbon dioxide, natural gas burns much cleaner than gasoline or diesel. This characteristic is particularly attractive in higher altitude cities like Bogotá where, as I've mentioned, particulate matter can be a real public health problem.

In addition to the environmental benefits, natural gas is also less expensive per unit of energy than gasoline. In Colombia, this is largely due to the four trillion cubic meters of natural gas reserves the country contains - a decent domestic supply. All of these benefits can be attained by a relatively low-cost conversion of a regular gas engine. Pretty cool.

A lot of other countries also have well developed systems to take advantage of their natural gas reserves. In South America, Argentina and Brazil have a few million CNG powered vehicles in their respective fleets - as do countries in other parts of the world, like Italy.

What I would like to know is this: if there is a cheaper, cleaner alternative to gasoline and diesel fuel, why all the dirty buses?