The following is an excerpt from Traffic by Tom Vanderbilt.

Why does the other lane always seem to be moving faster?

It is a question you have no doubt asked yourself while crawling down some choked highway, watching with mounting frustration as the adjacent cars glide ahead. You drum the wheel with your fingers. You change the radio station. You fixate on one car as a benchmark of your own lack of progress. You try to figure out what that weird button next to the rearwindow defroster actually does.

I used to think this was just part of the natural randomness of the highway. Sometimes fate would steer me into the faster lane, sometimes it would relinquish me to the slow lane.

That was until recently, when I had an experience that made me rethink my traditionally passive outlook on the road, and upset the careful set of assumptions that had always guided my behavior in traffic.

I made a major lifestyle change. I became a late merger.

Chances are, at some point you have found yourself driving along the highway when a sign announces that the left lane, in which you are traveling, will close one mile ahead, and that you must merge right.

You notice an opening in the right lane and quickly move over. You breathe a sigh, happy to be safely ensconced in the Lane That Will Not End. Then, as the lane creeps to a slow halt, you notice with rising indignation that cars in the lane you have vacated are continuing to speed ahead, out of sight. You quietly seethe and contemplate returning to the much faster left lane--if only you could work an opening. You grimly accept your condition.

One day, not long ago, I had an epiphany on a New Jersey highway. I was having a typical white-knuckle drive among the scenic oil-storage depots and chemical-processing plants of northern Jersey when suddenly, on the approach to the Pulaski Skyway, the sign loomed: LANE ENDS ONE MILE. MERGE RIGHT.

Seized by some rash impulse, I avoided the instinctual tickle at the back of my brain telling me to get in the already crowded right lane. Just do what the sign says, that voice usually counsels. Instead, I listened to another, more insistent voice: Don't be a sucker. You can do better. I plowed purposefully ahead, oblivious to the hostile stares of other drivers. From the corner of my eye I could see my wife cringing. After passing dozens of cars, I made it to the bottleneck point, where, filled with newfound swagger, I took my rightful turn in the small alternating "zipper" merge that had formed. I merged, and it was clear asphalt ahead. My heart was beating faster. My wife covered her face with her hands.

In the days after, a creeping guilt and confusion took hold. Was I wrong to have done this? Or had I been doing it wrong all my life? Looking for an answer, I posted an anonymous inquiry on Ask MetaFilter, a Web site one can visit to ask random questions and tap into the "hive mind" of an anonymous audience of overeducated and overopinionated geeks. Why should one lane move faster than the other, I wanted to know, and why are people rewarded for merging at the last possible moment? And was my new lifestyle, that of the late merger, somehow deviant?

I was startled by the torrent of responses, and how quickly they came. What struck me most was the passion and conviction with which people argued their various cases--and the fact that while many people seemed to think I was wrong, almost as many seemed to think I was right. Rather than easy consensus, I had stumbled into a gaping divide of irreconcilable belief.

The first camp--let us name it after the bumper sticker that says practice random acts of kindness--viewed early mergers as virtuous souls doing the right thing and late mergers as arrogant louts. "Unfortunately, people suck," wrote one Random Acts poster. "They'll try whatever they can to pass you, to better enjoy the traffic jam from a few car lengths ahead of you. . . . People who feel that they have more pressing concerns and are generally more important than you will keep going, and some weak-spined schmuck will let them in further down, slowing your progress even more. This sucks; I'm afraid it's the way of the world."

Another camp, the minority camp-let's call them Live Free or Die, after the license-plate motto of the state of New Hampshire-argued that the late mergers were quite rationally utilizing the highway's maximum capacity, thus making life better for everyone. In their view, the other group's attempts toward politeness and fairness were actually detrimental to all.

It got more complicated. Some argued that late merges caused more accidents. Some said the system worked much better in Germany, and hinted that my dilemma perhaps revealed some national failing in the American character. Some said they were afraid of not being "let in" at the last moment; some said they would actively try to block someone from merging, the way truckers often do. So what was going on here? Are we not all driving the same road, did we not all pass the same driving tests? What was puzzling was not just the variety of responses but the sense of moral righteousness each person attributed to his or her highway behavior, and the vitriol each person reserved for those holding the opposite view. For the most part, people were not citing traffic laws or actual evidence but their own personal sense of what was right.

I even found someone claiming to have had a conversion experience exactly the opposite of mine. "Until very recently, I was a 'late merger,' " wrote the author, an executive with a software company, in a business magazine. Why had he become a born-again early merger? "Because I came to realize that traffic flowed faster the sooner people merged." He used this as a metaphor for successful team building in corporate America, in which "late mergers" were those who consistently put their own opinions and motives above the greater company. "Early mergers," he wrote, could help push companies to their "maximum communal speed." But did traffic flow faster when people merged sooner? Or did it just seem more noble to think that it did?

You may suspect that getting people to merge in a timely fashion, and without killing one another, is less of a traffic problem and more of a human problem. The road, more than simply a system of regulations and designs, is a place where many millions of us, with only loose parameters for how to behave, are thrown together daily in a kind of massive petri dish in which all kinds of uncharted, little-understood dynamics are at work. There is no other place where so many people from different walks of life--different ages, races, classes, religions, genders, political preferences, lifestyle choices, levels of psychological stability--mingle so freely.

What do we really know about how it all works? Why do we act the way we do on the road, and what might that say about us? Are certain people predisposed to drive certain ways? Do women behave differently than men? And if, as conventional wisdom has it, drivers have become progressively less civil over the past several decades, why is that so? Is the road a microcosm of society, or its own place with its own set of rules? I have a friend, an otherwise timorous Latin teacher, who once told me how, in a modest Toyota Corolla, he had defiantly "stuck it" to the driver of an eighteen-wheeler who he felt was hogging the road. Some mysterious force had turned this gentle suburban scholar into the Travis Bickle of the turnpike. (Are you tailgatin' me?) Was it traffic, or had the beast always been lurking within?

The more you think about it--or, rather, the more time you spend in traffic with time to think about it--the more these sorts of puzzling questions swim to the surface. Why can one sit in traffic jams that seem to have no source? Why does a ten-minute "incident" create one hundred minutes of gridlock? Do people really take longer to vacate a parking spot when someone else is waiting, or does it just seem so? Do the car-pool lanes on highways help fight congestion or cause more of it? Just how dangerous are large trucks? How does what we drive, where we drive, and with whom we drive affect the way we drive? Why do so many New Yorkers jaywalk, while hardly anyone in Copenhagen does? Is New Delhi's traffic as chaotic as it seems, or does a beautiful order lurk beneath the frenzied surface?

Like me, you may have wondered: What could traffic tell us, if someone would just stop to listen?

Excerpted from Traffic by Tom Vanderbilt Copyright � 2008 by Tom Vanderbilt. Excerpted by permission of Knopf Canada, a division of Random House of Canada Limited. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.