Ellen Perlman was a GOVERNING staff writer and technology columnist.E-mail: firstname.lastname@example.org
About 50 years ago, arborists in Santa Monica, California, chose ficus trees for the urban landscape. The trees have large canopies that provide shade and oxygen, beautify the city and increase property values. The problem is that little ficus trees grow up to be big ficus trees--with roots that can break up sidewalks and leave the city vulnerable to pedestrian trip-and-fall litigation.
Municipalities around the country have faced this problem since they began pouring concrete sidewalks 125 years ago. Indeed, concrete slabs tend to suffocate tree roots, which then start to grow aggressively toward the surface. In the past, the remedy always has been to jackhammer the cracked sidewalk and pour new concrete.
A better solution for Santa Monica's ficus fiasco came to Richard Valeriano in a dream. The senior public works inspector had just spent a long day examining dozens of sidewalks along some of the city's 16,000 property parcels. That night, he dreamt of undulating sidewalks. He awoke wondering why they couldn't be made of a flexible material, instead of a brittle one. It took two years and a visit to a health club that was installing rubber floors for him to act on the idea. Six years ago, Santa Monica installed the first rubberized sidewalk panels and it is still testing their merits.
The trees clearly are faring better. Arborists speculate more water makes its way through the seams and some roots grow down, chasing the water. In addition, public works employees are able to lift the 2¥2 1/2 foot "slabs" with hand tools and peek underneath to see how the roots are growing. When they picked up the rubber after six years, they found roots that were a lot smaller than the ones under concrete. "It was pretty encouraging," says Valeriano.
So Santa Monica has branched out, laying rubber sidewalks in more than 60 locations. But other cities aren't exactly going out on a limb to test the new material. The rubber sidewalk in New Rochelle, New York, for instance, runs only 100 feet. Washington, D.C., has several blocks' worth. Altogether about 60 U.S. municipalities have installed stretches of sidewalk that are flexible and have some spring to them, similar to a rubberized running track.
Rubbersidewalks Inc., a California-based manufacturer, has put its product through a battery of tests. They've been shoveled, sanded and salted, and subjected to high heels, oil, acid, coffee, bicyclists, children, chalk and paint. The company has safety-tested them for people on skates, in wagons, with walkers, on crutches and on bikes. Gum, tree sap, berries and pollen can be hosed off or steam cleaned.
On the environmental front, rubber sidewalks not only are kinder to trees but are manufactured from recycled tires. The panels come in several different colors, but for the most part, engineers choose to buy them in a lovely shade of gray--although they tend not to exactly match the surrounding pavement.
Perhaps the biggest fans of the material are municipal risk managers and lawyers. In New Rochelle, where the sidewalks have been in place for two years, the tripping hazard around three trees has been greatly reduced. "The roots uplift the rubber sidewalks in a way that's still passable," says Jeff Coleman, commissioner of public works. "There's a nice gentle rise to them."
On the downside, they still need to be shoveled if they're covered in snow or ice. They can suffer cuts from knives and other tools, although the integrity of the sidewalk will not be affected. They can wear down a bit in heavily trafficked areas, but the sidewalks can be turned over and reused for many more years. Kids might be disappointed to learn that chalk marks don't last as long on the new rubber.
Initially, the cost for rubberized sidewalks is much higher than concrete. The 100-foot stretch in New Rochelle cost $8,000. Concrete would have cost $3,000. A lot of that has to do with the expense of shipping the heavy material from the factory in California, and cities buying just a few pieces, rather than in volume. The company is planning a second factory for New York State and thinks that if the sidewalks take off, the prices will come down.
But even at the higher initial prices, the equation changes in a few years when compared with the cost of having to remove and re-pour concrete. "After three years," Valeriano says, "we're not just breaking even, we're ahead of the game."