Excerpt from Valley 101: A Slightly Skewed Guide to Living in Arizona, a collection of Clay Thompson’s columns for The Arizona Republic. (Originally published July 16, 2003.)

Q: Does the rubberized asphalt being applied to the Valley freeways contribute to air pollution?

A: I put these matters to Matt Burdick, who knows all about stuff like this because he is a spokesman for the state Department of Transportation. He said not to worry.

About 10,000 old tires are recycled for every mile of rubberized asphalt that gets put down. However, according to Burdick, the overall amount of rubber in the asphalt is fairly small.

The rubber gets liquefied into an oil mixture and then is mixed in with the asphalt. That oil mixture accounts for about 10 percent of the weight of the stuff that ends up on the road, and only about 1 or 2 percent of that is rubber, Burdick said.

It is true that there is a certain amount of tire dust in the air. I think I did a column about that once. However, in the case of rubberized asphalt, the rubber is encapsulated in the asphalt so passing cars are not churning it into the air, Burdick said.