WASHINGTON - Pounding the pavement is getting a little easier on people's knees in many cities around the country. For reasons of safety and ease of maintenance, Washington and dozens of other communities are installing rubber sidewalks made of ground-up tires.

The rubber squares are up to three times more expensive than concrete slabs but last longer, because tree roots and freezing weather won't crack them. That, in turn, could reduce the number of slip-and-fall lawsuits filed over uneven pavement.

The shock-absorbing surface also happens to be easier on the joints of joggers, and more forgiving when someone takes a spill.

And the rubber sidewalks are considered more environmentally friendly: They offer a way to recycle some of the estimated 290 million tires thrown out each year in the U.S., and they do not constrict tree roots the way concrete slabs do.

"As our trees grow and mature sometimes the root systems begin to pull up the sidewalks," said Michelle L. Pourciau, acting director of the D.C. Transportation Department. "This is compromise between having a beautiful and healthy tree and having a safe and passable sidewalk."

Rubbersidewalks Inc. of Gardena, Calif., manufactures the small rubberized squares now being used on some sidewalks in more than 60 cities, including Washington.

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