Where Rubber Meets Road - NYTimes.com Q. With the millions of cars being driven billions of miles on American roads each year, why don't I see residue from their worn rubber tires along the roadside? What happens to all that rubber? A. While shreds from lost tires often show up along the highways, friction gradually wears the surfaces of most tires into a fine black powder. It unobtrusively blends with road dust and other automobile waste, like particles of motor oil. Waste like this rubber dust is considered a potential environmental problem when it washes off roads and ends up in streams and lakes. Such waste, when it pollutes bodies of water, is called nonpoint source pollution. What is left of the worn-down tires also presents a formidable bulk-disposal problem, the Environmental Protection Agency says. Even a decade ago, 290 million scrap tires were generated each year, making up 2 percent of the country's total solid waste. Some used tires are recycled, either in pieces or as ground rubber, and some end up in civil engineering uses like stabilizing road banks, but many end up being incinerated or burned for fuel. In properly designed burning facilities, the agency says, emissions are comparable to, and often lower than, those from conventional fossil fuels. C. Claiborne Ray