It may be the world's greatest public works project, but the United States interstate highway system doesn't inspire instant awe like the Great Wall of China, Egypt's pyramids and other man-made wonders.
Some may admire the 46,837-mile network as a breathtaking engineering feat, but for millions of commuters, vacationers and errand runners, it is a simply a convenience built for a society with a mania for motion.
But the interstate is remarkable for much more than its engineering. The system, which celebrates its 50th anniversary Thursday, has indelibly transformed American life -- for good and for bad.
"In the simplest terms, the interstate helped us to determine where we put our houses, our factories, how we transport our livestock and food products, and how much we can distribute," says William L. Withuhn, curator of transportation at the Smithsonian Institution's National Museum of American History, where an exhibit called America on the Move is on display.
The interstate "connects everybody to everything," says Alan E. Pisarski, a transportation policy analyst and author.
President Dwight Eisenhower signed the Federal-Aid Highway Act on June 29, 1956. On Wednesday, a cross-country caravan celebrating the interstate's birthday pauses for a ceremony in Frederick before pulling into Washington for Thursday's festivities. The convoy, sponsored by the American Association of State Highway and Transportation Officials, re-creates in reverse Eisenhower's journey as a young Army officer on a cross-country military expedition in 1919. According to highway folklore, the convoy, made mostly over dirt roads, convinced Eisenhower of the need for an expressway system.
But the interstate's roots are deeper.
Since a young George Washington took a path through Maryland's western mountains that would become the first National Road, a succession of leaders including Thomas Jefferson, Franklin D. Roosevelt and Harry S. Truman have advocated a highway network that would unite the sprawling nation.
The interstates "suggest all our dreams for what America might become -- one nation, indivisible, bound for all time by concrete and asphalt strands," writes Tom Lewis in Divided Highways: Building the Interstate Highways, Transforming American Life.
And yet, Lewis observes, "The very roads that we thought would unite us have sometimes actually divided us."
Every blessing attributed to the interstate has also spawned a curse, some critics say. Though conceived in the spirit of growth and unity, the highway's right of way laid waste to portions of cities and small towns across the country before the urban revolts of the 1960s and early 1970s checked unfettered construction.
While it opened all corners of the continental United States to visitors and growth, the interstate pushed much of the country's richly varied landscape off the map, as weary motorists stuck to the Econo Lodges and KFCs that proliferated near off-ramps.
And although interstates are regarded as twice as safe as secondary roads, they are now clogged precariously with satellite-tracked, 80,000-pound 18-wheelers racing to deliver perishable freight.
With limited access, wide shoulders, standardized signage and long straight-aways, the interstate is an ideal place to cruise along and ponder the ways it has changed our lives -- for better and for worse -- and to realize that freedom of movement has come at a price.
The interstate network was built in part as a response to the carnage caused by two-lane roads. "The interstate system is the safest road in the world," says Dan McNichol, author of The Roads that Built America: The Incredible Story of the U.S. Interstate System. Drivers are "twice as likely to make it alive."
The road's uniformity is what makes it safe. "You're never surprised by a grade or curve. Everything is designed to keep you alive -- the Jersey barriers, the median, the [rumble strips] that wake you up if you drift to the side of the road," notes McNichol.
Traffic accidents still cause tens of thousands of deaths each year, but without the interstates, many more would die.
"President Eisenhower 50 years ago was talking about more than 36,000 [annual] fatalities on the American highway system and how we had to address that. Now, 50 years later, we're at 43,000," says Pisarski.
That's terrible, Pisarski says, but, "keep in mind that there are millions of more motorists traveling much longer distances." Without the interstate, "you could talk about hundreds of thousands of people dying," he says.