Human beings are clever, bigheaded animals that have proved very formidable against predators like the now-extinct woolly mammoth and the near-extinct Bengal tiger. But we humans, particularly we modern humans, are also strangely vulnerable: fleshy, pudgy, and almost entirely bereft of natural defenses, such as thick outer shells, tusks, or sharp claws. Moreover, our gangly, awkward, injury-prone bodies are not particularly good at getting from place to place. Chimpanzees can at least swing from tree to tree — when was the last time you saw a human do that? It is thus a very good thing that we humans have SUVs, those hulking armored chariots that serve, in effect, as roomier and more menacing armadillo shells.

The automobile has changed the face of the world -- it has supersized our cities, it has generated an explosion of commerce and creativity, and it has brought our natural environment to the brink of collapse. But at a very basic level, it hasn't changed us. As Tom Vanderbilt vividly argues in Traffic (Random House, 416 pages, $24.95), his account of "how traffic explains the world," all the advanced automotive technology in the world can't change the fact that we are basically shaved monkeys.

To begin with, humans are social animals. And yet our range of communication on the road is severely limited. Say you honk at another driver because he has a Green Day bumper sticker and, hey, you like Green Day, too. Well, as Mr. Vanderbilt tells us, a Connecticut clergyman did exactly that, and the other driver flipped him the bird for all his trouble. It's hard to tell the friendly honk from the unfriendly honk, or whether someone is passing you out of malicious spite or, say, a desire to stay close to a friend leading him to an out-of-the-way bar mitzvah. Humanity's greatest gift, the capacity for language, is reduced to an only barely comprehensible grammar of crude gestures, flashing lights, and aggressive maneuvers. The end result is a level of alienation and anger that makes heavy traffic a punishing ordeal.

It is only natural that drivers call friends and family on their cell phones, to make enduring traffic a little easier. And the truth is that your individual crash risk only inches up a little when you're gabbing. The trouble is, as more drivers cocoon themselves in these diverting phone chats, the roads threaten to become far more dangerous. Driving requires a keen sense of what's going on around you: Your eyes need to dart around from mirror to mirror, yet you also need to keep your eyes ahead of you. You can try to compensate, but slowing down or hanging back won't necessarily save you.

As Mr. Vanderbilt briefly notes, Karl Benz, inventor of the gasoline-powered automobile and founder of the Benz Company, predicted that the market for automobiles would be limited by the small number of people with the instincts and skill it takes to do something as dangerous and demanding as driving a car. Benz had a point: Drivers tend to think they're doing a solid job if they don't actually crash. But what they ignore is that most drivers experience near misses all the time. Automobile manufacturers install seat belts and air bags and center high-mounted stop lamps to make us safer. And what happens? As economist Sam Peltzman first observed in 1976, these "safety features" do indeed make drivers feel safer. And so they "compensate" by driving more recklessly. It would be funny if it weren't so morbidly depressing.

One counterintuitive aid to safety, according to the late Dutch traffic visionary Hans Monderman, is to make the road seem more dangerous. Starting in the 1980s, Monderman began a series of experiments in rural Holland designed to make the "traffic world," which is governed by abstract signs, more like the "social world," which is governed by good manners. In the "traffic world," drivers want the road to themselves. Drivers really hate it when pedestrians are "all up in their grills," so to speak. They much prefer to have their pedestrians corralled on narrow sidewalks, crossing the street rarely, if ever, at carefully demarcated crosswalks complete with lights and signals. But in the "social world" model, drivers -- like kindergarteners -- have to learn how to share and play nicely with others. Monderman placed roads and sidewalks at the same level, and got rid of all stop signs and traffic lights. That way, drivers know that pedestrians might pop up at any time. There's no need for stop signs because drivers are always keeping an eye out for possible collisions. The less insulated from pedestrians and other unpredictable hazards drivers feel, Monderman argued, the slower and more carefully they are likely to drive. That's one reason why an Indian traffic specialist Mr. Vanderbilt talked to actually thinks cows on the road are a good thing. Because Indians are so reluctant to turn those venerated creatures into so much ground beef, they tread lightly on cow-heavy roads.

Traffic is full of these brilliant, unexpected little insights, which Mr. Vanderbilt weaves together from a wide range of sources, from social scientists to grizzled veterans of the traffic wars. What it doesn't offer is a central insight. As a Monderman admirer, I had hoped that Mr. Vanderbilt would build on the logic of Monderman's "traffic-calming" strategies to make a broader point about human societies. Traffic engineers of the past tried to tame the anarchy of the road through superior road design and stiff penalties. And there's certainly something to be said for both: Nanny-statism on the highway has given us the rumble strip, speed bumps, and other lifesaving innovations. But it turns out that one key to smooth, free-flowing traffic is drivers who fear for their lives as much as pedestrians in Houston.

Mr. Vanderbilt has written Traffic in the vein of the guaranteed best seller -- the book is even-tempered and studiously universal, taking care to remain as relevant for British or Armenian or Japanese readers as it is for American readers. He steers clear of the great debate of our time -- that is, is the automobile an instrument of human freedom or of environmental and cultural destruction? Right now, energy prices are the central domestic issue in American politics. Voters consider the price of gas a more vital question than the fate of Iraq. And for good reason: The high price of gas raises the possibility that we will start organizing our lives and our economy very differently. Already you see a thickening of our edge cities, and a slight but noticeable uptick in telecommuting. A few brave souls have started bicycling in Los Angeles, an event that until recently would have struck a local as a harbinger of the apocalypse. As more and more drivers curb their driving habit, there is a real possibility that we won't be able to raise enough gas-tax revenue to maintain our crumbling highways. You get the sense that the way we move from place to place is about to undergo a phase shift - - as big as the transformation wrought by the Internet, and certainly bigger than the fad for hybrid vehicles. Mark my words: Within 10 years, we may all be riding Segways. When it happens, remember that you read it here first.