If you’ve ever traveled in Central America, you’ve seen the “chicken buses”: They’re old U.S. school buses, decorated to varying degrees of flamboyance, slightly repurposed to transport people, goods, and in some rural areas, chickens (and other live animals).
“At first glance, it seems like an environmental victory to squeeze the maximum life out of such equipment, the automotive equivalent of sending old sweaters to Goodwill,” writes Terri Peterson Smith in E Magazine. But these buses’ emissions—nitrogen oxide, soot, and other contaminates—pollute the air and can cause health problems.
The problem is worst with the oldest buses, according to the article, which cites an Environmental Protection Agency (EPA) finding that "pre-1990 buses may emit up to six times more pollution than newer models."
Source: E Magazine