Every year, billions of vehicles worldwide shed an estimated 6 million tons of tire fragments. These tiny flakes of plastic, generated by the wear and tear of normal driving, eventually accumulate in the soil, in rivers and lakes, and even in our food. Researchers in South China recently found tire-derived chemicals in most human urine samples.
<sarcasm> but if more people were walking, they would all be run over by tiny men in Dodge Ram250s</sarcasm>