By Bruce Kennedy
CNN Interactive

At the turn of the 20th century, automobiles were coming into their own as convenient and efficient transportation -- but they were still considered a novelty. In 1900, there were only about 8,000 cars on U.S. roads.

But as automotive technology progressed, many roads in the early 1900s remained little more than glorified dirt tracks. A U.S. military officer of the time summed up road conditions:

"In many parts of the United States the roads are torn up with the outcoming frost in the spring, soaked with autumn rains, frozen into ridges in winter, and buried in the dust in the summer, making four regular seasons of bad roads."

The first complete survey of America's roads, finished in 1904, reported that of the more than 2 million miles of rural public roads then existing in the country, fewer than 154,000 miles were "surfaced" -- with either gravel, stones or crude paving materials.

Most intercity travelers took trains. For car drivers venturing outside major cities, travel was a perilous experience -- mostly due to unpaved and unpredictable roads.

Between 1908 and 1916, with the advent of the mass-produced Ford Model T and other "motor buggies," the number of cars in America increased about 500 percent, to nearly 2.5 million.

That automotive explosion also brought pressure on the government to improve its road and highway systems. Even the best-constructed roads at the century's start began to disintegrate under the weight, constant pounding and unprecedented speeds of the automobile.

"People experimented with all sorts of things (as paving material)", says Richard Weingroff of the U.S. Federal Highway Administration. "In Maryland, for example, they experimented with oyster shells -- which they had a lot of. In the South they tried to bind cotton into roads."

Asphalt, a derivative of oil, had been around for centuries -- and was used as an early road-paving material. But it was in short supply in the United States in its natural form.

Gasoline, however, was to supply the solution. In the early 1900s, the gas used to power most American cars was a byproduct of the distillation of kerosene from petroleum. One of the other byproducts was bitumen -- a key ingredient of asphalt. As the number of U.S. cars increased, so did the production of gasoline -- and, along with it, asphalt.

Concrete also became popular as a road-paving surface. Wayne County, Michigan, is believed to be the first rural area in the United States to pave a road with concrete. The concrete for that mile-long stretch of Woodward Avenue was laid down in 1909.

Ten years later, Lt. Col. Dwight Eisenhower was an observer on the U.S. Army's first transcontinental convoy of military vehicles. The convoy's trip from Washington to San Francisco took two months -- due mostly to appalling road conditions. The arduous and uncomfortable trip would have a profound impact on the future president.

Improved roads also meant radical changes in automobile design.

"The Model T Ford unveiled in 1908 was the perfect car for its time," says Weingroff. "It was high and lightweight, so it could get through ruts. And in an era before service stations and auto mechanics, it was durable and yet simple enought for the owner to repair. Two decades later, the roads have improved and the Model T is an antique. Who needs an uncomfortable Model T, when you can get a much sleeker car, lower to the ground?"

The Great Depression of the 1930s brought about the U.S. Works Progress Administration -- whose mission was to create jobs for millions of unemployed workers. Under the WPA, workers helped improve America's roadways -- building 75,000 bridges and constructing or improving more than 650,000 miles of public roads.

Meanwhile, Adolf Hitler was creating in Germany what many consider the ultimate highway of its time -- the autobahn. That road system helped Germany fight on two fronts during World War II. It also aided advancing Allied troops in their defeat of the Nazis.

Eisenhower, then Supreme Allied Commander, witnessed the autobahn system firsthand -- and was further convinced of the need to improve his nation's roads.

"The old (1919) convoy had started me thinking about good, two-lane highways," he said, "but Germany had made me see the wisdom of broader ribbons across the land."

In 1956, then-President Eisenhower signed into law the Federal Aid Highway Act, which led to more than 45,000 miles of uniform, interstate highways -- the largest peacetime construction project ever undertaken.

"The amount of concrete poured to form these roadways would build 80 Hoover Dams or six sidewalks to the moon," Eisenhower later recounted.

"To build them, bulldozers and shovels would move enough dirt and rock to bury all of Connecticut two feet deep. More than any single action by the government since the end of the war, this one would change the face of America with straight-aways, cloverleaf turns, bridges and elongated parkways," Eisenhower wrote. "Its impact on the American economy -- the jobs it would produce in manufacturing and construction, the rural areas it would open up -- was beyond calculation."

As the century ends, many people are still calculating the impact highways have had on America's physical and psychological landscape. Humorist Dave Barry recently summed up much of America's ambivalence toward highways, when he described the experience of traveling cross-country as a child:

"We saw a lot of the country, but we actually didn't touch any of it."