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In Europe, by contrast, maintenance and repair work begin before damage is even visible. During a 1990 study trip to Europe, a group of U.S. civilian and government experts was amazed to see maintenance work under way on highways considered to be in superb condition by American standards.
Given the emphasis on new construction, U.S. highway designers have badly neglected research and development, which might have kept the roads abreast of mounting traffic. "For many years, the Department of Agriculture spent more % researching dog food than the Department of Transportation did on highways," says Thomas Deen, executive director of the Transportation Research Board. Europeans routinely spend 20 times as much per capita on R. and D. Contractors in Europe add innovative polymers to asphalt and mix new additives into concrete. One additive developed in France -- based on a complex polymer akin to shredded Tupperware plastic -- increased construction costs 8% while doubling the life of a road.
But some of the most important differences between American and European expressways lie well beneath the surface. All highways are built by bulldozing softer subsoils and either tamping them or replacing them with more durable dirt or gravel. But in Germany the roadbeds tend to be 1.5 m or 1.8 m (5 ft. or 6 ft.) deep, twice the U.S. average. European engineers also devote more time and money to designing roadbeds that resist frost and have excellent drainage, addressing two problems that play havoc with U.S. thoroughfares. Each step, from laying the subsequent gravel or concrete layer to applying the asphalt surface, is taken with long-term durability in mind.
In the past few years, U.S. engineers and contractors have begun to apply some of the lessons from overseas, particularly in improving materials. Asphalt, a heavy petroleum residue that is typically mixed with crushed rock or even slag from steel mills, can be made much stronger and more durable by adding various polymers, including polyurethane. About half of new roads are built with asphalt (the other half are concrete), and nearly 90% of resurfacing jobs employ the sticky material.
American contractors are gradually introducing stone-matrix asphalt, a surfacing mixture embedded with uniformly sized rocks that help the material hold together better and last longer. Road technicians are also experimenting with a more porous asphalt that provides an anti-skid surface and has the added benefit of reducing noise. And to cut costs, builders have developed imaginative ways to recycle old chunks of asphalt.
Concrete -- a mixture of cement, sand and gravel -- has also been enhanced. A slew of additives, such as fine steel or urethane fibers, have toughened the product and lengthened its service life. To minimize traffic disruptions during repair, some quick-drying concretes cure so rapidly that highways can be opened to traffic within an hour. New bonding techniques enable concrete to adhere to old concrete slabs, which means the old layers don't have to be laboriously removed. U.S. contractors have begun to use new equipment that accelerates the laying process, including one colossus that spews out two parallel 3.7-m-wide (12-ft.-wide) strips of wet concrete like newspapers off a press.