Like HowStuffWorks on Facebook!

How do different types of roads affect the environment?


Ubiquitous Asphalt

Ninety-six percent of America's paved roadways are asphalt, a substance composed of molecules, mostly polynuclear aromatic hydrocarbons, extracted from crude oil at the refinery.

To build an asphalt road, the material (5 percent asphalt and 95 percent sand and gravel) is heated to 300 to 400 degrees Fahrenheit (148 to 204 degrees Celsius) in a truck's rotating hopper, poured over gravel and smoothed using a spreading machine. Asphalt hardens as it cools.

Asphalt is a surface water can't seep through, and runoff of chemicals such as zinc, copper, rust and cadmium, enters water tables, streams and rivers where that unfiltered runoff can poison aquatic life, taint drinking water and introduce E-Coli bacteria, too, making waters unsafe for recreation.