As Gottlieb Daimler and Karl Benz were developing their early auto designs in the late nineteenth century, engineers struggled to build roads that could accommodate the carriages and cars of a mobile society. The existing network of crude dirt and stone paths was notorious for snapping axles and swallowing cars in thick mud. In America, engineers explored bricks, wood planks, and metal rails before settling on pavement.
Asphalt first arrived in the United States in Newark, New Jersey, in 1870. Concrete was already in use as a base below brick and stone roads, but it wasn't until 1891 that cement was poured as a city street surface in Bellefontaine, Ohio.
Today, asphalt and concrete receive equal consideration by engineers. Improvements in pavement technology have largely eliminated the ruts that once plagued asphalt and cracks that spoiled concrete. Choosing a material is a matter of economics that considers life span, maintenance requirements, and road closure time.
"In heavy traffic, concrete has a tendency to win out, and asphalt tends to be used with lower traffic," says Curtis Bleech, an engineer with the Michigan Department of Transportation. "But you can design asphalt or concrete to perform in any environment."
In Michigan - where perpetual repairs might lead you to peg the life span of a road at three months - engineers expect a freeway to last thirty-five years, whether it's made of concrete or asphalt. Price tags vary based on the project, but building a two-lane highway from scratch costs about $2 million per mile using either material.
Although concrete receives equal consideration, more than 90 percent of America's 2.6 million miles of paved roads are surfaced in asphalt. Increasingly, composite roads are used as a cost-effective method of rehabbing fatigued pavement. With this technique, smooth asphalt is layered over worn but stable concrete.