by Whit Gibbons

June 1, 2008

The population of the United States is approximately 300 million people, a number exceeded only by China and India. But this column is not about human population, where we rank third. It's about our automobile tire population, where we rank first. Each year we discard more than 270 million tires, which weigh more than 3.5 million tons. The average person adds a tire or so to the scrap pile every year.

Considering the quality of tires on cars when I was a kid, my guess is that even in a good year each driver added two or three tires to the world supply. Back then, old tires were used for three things. We rolled them down hills to see how far they would go. We burned them outside while standing around talking on a cold night. And we made tire swings. As my childhood progressed, people who lived at the bottom of hills gradually discouraged the first idea. The second idea was squelched by people without completely blocked sinuses who decided it was better to be cold than to smell burning rubber. Tire swings lived on. I even put one up in the backyard for my own children.

With the numbers for scrap tires having been stacked to absurdly high levels, ideas for new ways to dispose of or recycle old rubber are understandably proliferating. How about just discarding the tire at the city dump? In the majority of states you might consider that if the dump happens to be at the bottom of a hill so you can roll the tire down to it--and if it's nighttime so no one is watching you. Because in more than thirty states, taking old tires to a landfill is illegal. The rest of the states are likely to have similar restrictions soon.

So what are we supposed to do with this ever-growing supply of hard rubber circles that would almost reach the moon if they were stacked on top of each other? Turns out that between 5 and 10 percent of our excess tires are exported to other countries. Let's not even try to guess why another country would want tires without cars attached to them, but those are the facts. Maybe they have a lot of people with head colds who spend lots of time outside talking on cold nights.

Actually, burning rubber is not out of the question as a recycling mechanism. Old tires have provided an alternative source of fuel for U.S. industries in which water must be heated to run power plants, pulp mills, and cement plants. As many as 40 percent of our discarded tires are used this way in some years.

The most promising use of discarded tires is a true recycling venture that creates walkways, playground pads, and other forms of ground or floor covering from old tires. Some people maintain that a pad made of shredded rubber has the potential to catch on fire from a burning cigarette or dropped match, but mixing in a nonflammable substance could solve that problem. Another use of shredded rubber tires is to supplement asphalt used for paving streets, a fitting final resting place for an old tire.

One of the most controversial uses of recycled tires is to make mulch for landscaping and gardening. In a steel-belted radial tire for a passenger car, the steel itself makes up as much as 10 percent of the tire's weight, and the steel fibers are often coated with zinc to retard the rate of rusting. The metals are in the discarded tires, and excessive zinc can hinder plant growth. Whether the zinc level in an average tire is something to be concerned about for plants in a landscaped lawn or, more importantly, in an agricultural situation, has yet to be determined. Studies should be undertaken to assure that tire recycling efforts can proceed safely.

Meanwhile, we always have the option of making tire swings from the remaining surplus. We have enough tires for every man, woman, and child to have a personal swing. Anything else we use old tires for will be a bonus.

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