Traffic_ Why We Drive The Way We Do Part 4

For each of the different radio stations for which Hughes reports, he must change the length of his report, as well as the way he says it. One station wants "upbeat and conversational," while another wants a precise robotlike diction they call "traffic formatics." Some stations have advertis.e.m.e.nts for Hooters Casino, but the Christian stations do not. Some stations actually want him to be someone else. "Good morning, I'm Jason Kennedy with AM 1150 traffic brought to you by Air New Zealand," I suddenly hear him say. "They're sort of competing stations," he explains sheepishly, "even though we own them both." morning, I'm Jason Kennedy with AM 1150 traffic brought to you by Air New Zealand," I suddenly hear him say. "They're sort of competing stations," he explains sheepishly, "even though we own them both."

Hughes has an instinctual understanding of Los Angeles' highways. He can tell which way a rainstorm is moving by looking at the real-time traffic-flow highway maps. He knows Fridays heading east out of the city can be particularly bad. "Everyone's going to Las Vegas-all the way to ten p.m. that'll be backed up." He knows that people drive slower on highway stretches that have sound barriers to either side. He knows that mornings with heavy rains often lead to lighter afternoon traffic. "Maybe a lot of people got scared of the rain and disappeared," he says. He notes that while traffic information is easily available to the public, often the trick is in understanding it. "It's kind of like The Matrix, The Matrix," he says. "You're looking at the map and you can pick out what looks right and what doesn't. I can look at the map now and say, 'Hey, there's something wrong on the 101. A big-rig fire at Highland, probably.'"

There is no limit to the things that can disrupt the flow on Los Angeles highways. "Do you want to know the number one specific item dropped on the freeway?" asks Claire Sigman, another Airwatch reporter. "The most recorded item is ladders." Trucks, just like in the Beverly Hills Cop Beverly Hills Cop movies, also spill avocados and oranges. Portable toilets have been dumped in the middle of the freeway. In 2007, a house, replete with graffiti and a "For Rent" sign, sat for weeks on the Hollywood Freeway, abandoned during the course of its move after it struck an overpa.s.s (the owner had taken a detour onto an unauthorized route). People hold apocalyptic signs on overpa.s.ses, or threaten to jump. Wildfires break out. Out in the high desert, tumbleweeds cause problems. "People swerve out of the way, rather than just drive through it," Hughes says. A computer screen at the Airwatch office ticks off a steady flow of traffic incidents, ranging from the absurd to the horrifying, as recorded by the California Highway Patrol (CHP). Codes are used to disguise the presence of stalled female drivers, who might otherwise be preyed upon by unsavory men listening to police scanners. Not atypical of the stream is incident 0550, which describes a "WMA," or white male, wearing a plaid jacket and "peeing in middle of fwy." It adds a noteworthy detail: "No veh in sight." (Now, where was that wayward Porta Potti?) movies, also spill avocados and oranges. Portable toilets have been dumped in the middle of the freeway. In 2007, a house, replete with graffiti and a "For Rent" sign, sat for weeks on the Hollywood Freeway, abandoned during the course of its move after it struck an overpa.s.s (the owner had taken a detour onto an unauthorized route). People hold apocalyptic signs on overpa.s.ses, or threaten to jump. Wildfires break out. Out in the high desert, tumbleweeds cause problems. "People swerve out of the way, rather than just drive through it," Hughes says. A computer screen at the Airwatch office ticks off a steady flow of traffic incidents, ranging from the absurd to the horrifying, as recorded by the California Highway Patrol (CHP). Codes are used to disguise the presence of stalled female drivers, who might otherwise be preyed upon by unsavory men listening to police scanners. Not atypical of the stream is incident 0550, which describes a "WMA," or white male, wearing a plaid jacket and "peeing in middle of fwy." It adds a noteworthy detail: "No veh in sight." (Now, where was that wayward Porta Potti?) CHP officers are the foot soldiers in the daily battle to keep Los Angeles' traffic from collapsing. The sophisticated computer modeling and fiber-optic cable that the traffic generals in the bunker have at their disposal are of little use when a car has stalled on Interstate 5, as I learned one afternoon when I went out for a patrol in a CHP cruiser with Sergeant Joe Zizi, an easygoing former trooper now doing public relations. CHP patrol officers begin each day by "cleaning their beat," or removing any abandoned vehicles or hazards from the road. "That way there's nothing that people have to look at when they're driving," Zizi says as he drives along the 101. Something as simple as a couch dumped in a roadside ditch can send minor shudders of curiosity through the traffic flow. A standard-issue black pump-action shotgun sits between the front seats. To enable drivers to carry out their traffic triage duties, patrol cars are outfitted with reinforced b.u.mpers, designed to let them push cars off the road rather than wait for a tow truck. Their trunks are filled with a dizzying array of equipment for dealing with traffic contingencies, ranging from baby-delivering kits ("definitely a spectacle for rubberneckers") to dog snares.

"For some reason, dogs are attracted to the freeway," says Zizi. "They get on there, get completely freaked out, and start running down the center." According to CHP statistics, these Code 1125-As (traffic hazard-animal) peak on July 5, presumably from dogs scared by the previous night's fireworks. When traffic is moving, CHP officers pa.s.s the time by looking for stolen vehicles (screwdrivers in the ignition are a telltale sign) and, of course, writing traffic tickets. Does Zizi have any advice for beating tickets? "I have a lot of officers who say that women crying will get them out of tickets, while other officers say that if someone does does cry they're getting the ticket," he says. "Of course we have a lot of men who cry trying to get out of tickets, but that really doesn't work on the heartstrings of officers." cry they're getting the ticket," he says. "Of course we have a lot of men who cry trying to get out of tickets, but that really doesn't work on the heartstrings of officers."

For all the Caltrans cameras and loops wired into the road, for all the CHP officers flagging incidents, the highway system running through Los Angeles is so vast and incomprehensible that, sometimes, the only way to really understand what's happening is to pull way back and view the whole system from above. That is why there is still a place for people like Mike Nolan, KFI's "eye in the sky," a longtime L.A. traffic reporter who, twice daily, will take off in his Cessna 182 from Riverside County's Corona Airport and cover a swath of ground from Pasadena to Orange County.

"The learning curve is being able to read a freeway," he explains, banking his plane over a new subdivision carved into green hillside. "I know what's normal. I know where it should be slowing down and where it shouldn't. When I see something out of the ordinary, then I investigate it." Nolan, whose navigational mantra is "Keep the freeway to your left," knows traffic patterns like a grizzled fis.h.i.+ng guide knows the best ba.s.s holes. A stalled Volkswagen in East Los Angeles is worse than an overturned oil truck in La Canada ("More spectacular does not necessarily translate into worse," he says). Mondays, especially during Monday Night Football, Monday Night Football, tend to be a bit lighter. Thursday, congestion-wise, is now looking like the new Friday, traditionally the busy "getaway day." There are also strange blips in the pattern, like sunrise slowdowns. "The very first day of standard time, when we go from daylight saving time to darkness, everybody just locks up," he says. "The traffic goes from bad to horrendous." Rainy days can be bad, but the first rainy day in a while is even worse. "There's a buildup of oil and rubber if it hasn't rained in a while. It's like driving on ice, literally." tend to be a bit lighter. Thursday, congestion-wise, is now looking like the new Friday, traditionally the busy "getaway day." There are also strange blips in the pattern, like sunrise slowdowns. "The very first day of standard time, when we go from daylight saving time to darkness, everybody just locks up," he says. "The traffic goes from bad to horrendous." Rainy days can be bad, but the first rainy day in a while is even worse. "There's a buildup of oil and rubber if it hasn't rained in a while. It's like driving on ice, literally."

Nolan says people have long been predicting, because of ground sensors and in-vehicle probes that can detect the speed of traffic, that there will no longer be a need for aerial traffic reports. Indeed, on his instrument panel he has attached a TrafficGauge, a Palm Pilotsized device fed by Caltrans data, that shows congestion levels on L.A. freeways. But he says that data rarely tell the whole story, or the correct story. "In my mind there's no subst.i.tute for looking out the window and telling people what you've got," he says. "The sensors in the road are delayed, they're inefficient. They're working half the time, not working half the time. There's no subst.i.tute for saying, 'It's in the right lane, I see it right there, right at the fill-in-the-blank overpa.s.s.' Or that the tow truck is in heavy traffic. The sensor can't tell you the tow truck's a block away, or ready to hook up and pull away. It can't give you the substantive info that comes from looking at it directly."

Indeed, that afternoon of flying around the city, accompanied by an Airwatch reporter receiving ground reports, seems to be an exercise in chasing ghosts. The jackknifed tractor-trailer on the 710 is not there, or never was there. The blockage on the 405 was a rumor. Nolan is the one who must try to make sense of the strange reports that come in, like the one that announced a dead dog was "blocking lanes one, two, three, and four." The most remarkable traffic event he ever saw was during the L.A. riots of 1992. "I remember seeing people stop at a stoplight in Hollywood. They would get out and loot a store. The light would turn green and they'd get back in and drive away. That was the most incredible thing I've ever seen."

Flying over a city like Los Angeles, it is easy to glance down and think, for a moment, that the people below, streaming along trails, look like ants. If only it were that simple.

When Slower Is Faster, or How the Few Defeat the Many: Traffic Flow and Human Nature You hit the brakes for a second, just tap them on the freeway, you can literally track the ripple effect of that action across a two-hundred-mile stretch of road, because traffic has a memory. It's amazing. It's like a living organism.

-Mission: Impossible III

At some point you may have come to a highway on-ramp, expecting to join the flow of traffic, only to be stopped by a red light. Such devices are called ramp meters, and they are found from Los Angeles to South Africa to Sydney, Australia.

Ramp meters often seem frustrating because the traffic on the highway appears to be moving just fine. "People ask me, 'How come you're stopping me at the ramp meter? The freeway is free-flowing,'" says Dawn Helou, the Caltrans engineer. "The freeway is free-flowing because you're stopping."

This is one of the most basic, and often overlooked, facts about traffic: That which is best for an individual's interest may not be best for the common good. The game traffic engineers play to fight congestion involves fine-tuning this balance between what is "user optimal" and what is "system optimal." This happens on several different levels, both having to do with congestion: how traffic moves on roads and how larger traffic networks behave (an idea I'll return to in a later chapter).

The reason why highway ramp meters work is, on the face of it, simple once one knows a few basic facts about traffic flow. Engineers have been trying to understand, and model, traffic flow for many decades, but it is a huge and surprisingly wily beast. "Some puzzles remain unsolved," declares Carlos Daganzo, an engineer at the University of California, Berkeley. The first efforts merely tried to model the process known as "car following." This is based on the simple fact that the way you drive is affected by whether or not someone is in front of you, and how far away or close they are. Like ants responding to the presence of pheromones on the trail, you're influenced by the driver ahead, a constant, unsteady wavering between trying not to get too close and trying not to slip too far back. Now imagine those interactions, plus lane s.h.i.+fts and all the other driving maneuvers, a fluctuating mix of vehicle speeds and sizes, a wide range of driver styles and agendas, a dizzying spectrum of differing lighting and weather and road conditions; then multiply all this by the thousands, and you can begin to appreciate the higher-order complexities of traffic modeling.

Even the most sophisticated models do not fully account for human weirdness and all the "noise" and "scatter" in the system. Traffic engineers will offer caveats, like the disclaimer I saw at one traffic conference: "This model does not account for the heterogeneity of driver behavior." Do you feel uncomfortable driving next to someone else, and therefore speed up or slow down? Are you sometimes willing, for no apparent reason, to ride quite close to the car in front, before gradually drifting back? All kinds of strange phenomena lie outside easy capture by the traffic sensors. Car following, for instance, is filled with little quirks. A study that looked into how closely pa.s.senger-car drivers followed SUVs found that car drivers, contrary to what they said they did-and despite the fact that the SUV was blocking their view of the traffic ahead-actually drove closer to SUVs than when they followed pa.s.senger cars.

Or take what Daganzo has called the Los Gatos effect, after an uphill stretch of highway in California. You may have experienced this: Drivers seem reluctant to abandon the pa.s.sing lane and join the lane of trucks chugging uphill, even when they are being pressured by other drivers, and even when the other lane is not crowded. What's going on? Drivers may not want to give up the fast lane for fear of having trouble returning to it. They may also be unsure whether the person behind truly wants to go faster or is just keeping a tight s.p.a.ce to prevent someone else from pa.s.sing. A tight "platoon" forms, but for how long? We all see these odd patterns. One of the idiosyncrasies I have noticed in traffic flow is something I call "pa.s.sive-aggressive pa.s.sing." You're in the pa.s.sing lane when suddenly the driver behind you pressures you to move into the slower right-hand lane. After you have done so, they then move into your lane, in front of you, and slow down, thus forcing you you to pa.s.s to pa.s.s them. them.

The basic parameters of how highways perform have been gradually hammered out. One of the key performance measures is volume, also called flow, or the number of vehicles that pa.s.s a buried sensor or some other fixed point on the highway. At four a.m., before rush hour, cars may be zipping along a highway at 75 miles per hour. The volume is measured at 1,700 cars moving past a point in one hour. As rush hour begins, the volume quite naturally begins to rise in an upward curve, reaching a theoretical maximum of 2,400 cars traveling at 55 miles per hour. System-wise, this is traffic nirvana. Then, as additional vehicles enter the highway, the curve begins to drop. Suddenly, the volume is back at 1,700. This time the cars are going 35 miles per hour. "So you have the two 1,700s," Helou says. "Same volume, completely different situation."

Because traffic moves in time and s.p.a.ce, measurements like volume can be deceiving, as can the highway itself. Solo drivers sitting in a highly congested lane may look to the HOV lane next to them and think that it's empty-a psychological condition so prevalent it even has a name, "empty lane syndrome." Many times it just seems empty because of the large headways between vehicles moving at much higher speeds. That lane may actually be achieving the same volume as the lane you are in, but the fact that the drivers might be going upward of 50 miles per hour faster creates an illusion that it's being underused. Of course, neither of these positive or negative individual outcomes-the driver whisking along at 80 miles per hour or the people stuck at 20 miles per hour in the congested lanes-are what's best for the entire system. The ideal highway will move the most cars, most efficiently, at a speed just about halfway.

Even as rush hour kicks in and the speed-flow curve begins to drop, traffic can perk along at what has been called "synchronized flow," heavy but steady. But as more vehicles pile onto the highway from on-ramps, the "density," or the number of cars actually found in a one-mile stretch (as opposed to pa.s.sing a single spot), begins to thicken. At a certain point, the critical density (the moment, you will recall from before, when the locusts began their coordinated march), the flow begins to break down. Bottlenecks, fixed or moving, squeeze the flow like a narrowing pipe. There are simply too many cars for the road's capacity.

Ramp metering aims to keep the highway's "main-line flow" below the critical density by not letting the system be flooded with incoming on-ramp cars. "If you allow unimpeded access, then you have a platoon of vehicles that are entering the main line," says Helou. This means not only more cars but more cars jockeying to merge. Studies have shown that this is neither predictable nor always cooperative. "That [merging] eventually breaks down the right lane," she says. "This overflows to the next lane, because people try to merge left before they get to it. And then the people in the second lane try to merge to the next lane before they get to it, so you break down the whole freeway." A line of cars waiting to exit an off-ramp can trigger this same chain reaction, one study showed, even when all the other lanes were flowing nowhere near critical density.

If done properly, ramp metering, by keeping the system below the critical density, finds that sweet spot in which the most vehicles can move at the highest speed through a section of highway. Engineers call this "throughput maximization."

A simple way to see this in action involves rice. Take a liter of rice and pour it, all at once, through a funnel and into an empty beaker. Note how long it takes. Next, take the same rice and pour it not all at once but in a smooth, controlled flow, and time that process. Which liter of rice gets through more quickly? In a demonstration of this simple experiment by the Was.h.i.+ngton DOT, it took forty seconds for one liter of rice to pa.s.s through the funnel using the first method. The second method took twenty-seven seconds, nearly one-third less time. What seemed slower was actually faster.

Rice has more to do with traffic than you might think. Many people use water a.n.a.logies when talking about traffic, because it's a great way to describe concepts like volume and capacity. One example, used by Benjamin Coifman, an engineering professor at Ohio State University who specializes in traffic, is to think of a bucket of water with an inch-wide hole in the bottom. If the inflow into the bucket is half an inch in diameter, no water will acc.u.mulate. Raise it to two inches, however, and the water rises, even though some water is still exiting. Whether we drive into a jam (or a jam drives into us) depends on whether the "water"-that is, the traffic trying to flow through a bottleneck-is draining or rising. "As a driver, the first thing you encounter is the end of the queue," Coifman told me. "The first thing you encounter is wherever the water level happens to be that day." The bucket metaphor also teaches us something else about traffic: No matter how much capacity there is in the rest of the bucket (or on the roads), the size of the hole (or the bottleneck) dictates what gets through.

At places like bottlenecks, however, traffic acts less like water (it does not speed up as highway "channels" narrow, for one) and more like rice: Cars, like grains, are discrete objects that act in peculiar ways. Rice is what's called a "granular media," a solid that can act like a liquid. Sidney Nagel, a physicist at the University of Chicago and an expert in granular materials, uses the a.n.a.logy of adding a bit of sugar to a spoon. Pour too much, and the pile collapses. The sugar flows like a liquid as it collapses, but it's really a group of interacting objects that do not easily interact. "They do not attract one another," says Nagel. "All they can do is scatter off one another." Put a bunch of granular materials together, and it is not easy to predict how they will interact. This is why grain silos are the building type most p.r.o.ne to collapse, and it's also why my box of Cascadian Farm Purely O's cereal begins to bow outward at the bottom after several pours.

Why does the rice jam up as you pour it into the funnel? The inflow of rice exceeds the capacity of the funnel opening. The system gets denser and denser. Particles spend more time touching one another. More rice touches more rice. The rice gets "hung up" from the friction of the funnel walls. Sound familiar? "That's like cars on the highway," says Nagel. "And when you get narrowing of traffic, then that becomes very much stuff trying to flow through the hopper."

Pouring less rice at a time-or moving fewer cars-keeps more s.p.a.ce, and fewer interactions, between the grains. Things flow faster. As intuitive as the "slower is faster" idea is, it's not always easy for a driver stuck in traffic to accept. In 1999, a state senator from Minnesota, claiming that ramp metering in the Twin Cities was doing more harm than good, launched a "Freedom to Drive" proposal that called for, among other things, shutting down the meters. The legislation died, but under another bill a ramp-meter "holiday" was declared. For two months the meters were turned off. Drivers could enter the highway at will, on so-called sane lanes, unfettered by troublesome red lights. And what happened? The system got worse. Speeds dropped, travel times went up. One study showed that certain highway sections had double the productivity with ramp meters than without. The meters went back on.

The "slower is faster" idea shows up often in traffic. The cla.s.sic example concerns roundabouts. Many people are under the mistaken impression that roundabouts cause congestion. But a properly designed roundabout can reduce delays by up to 65 percent over an intersection with traffic signals or stop signs. Sure, an individual driver who has a green light may fly through a signalized intersection much more quickly than through a roundabout. Roughly half the time, however, the light will not be green; and even if it is green there is often a rolling queue of vehicles just starting up from the previous red. Add to this such complications as left-turn arrows, which prevent the majority of drivers from moving, not to mention the "clearance phase," that capacity-deadening moment when all all lights must be red, to make sure everyone has cleared the intersection. Drivers do have to slow down as they approach a roundabout, but under typical traffic conditions they rarely have to stop. lights must be red, to make sure everyone has cleared the intersection. Drivers do have to slow down as they approach a roundabout, but under typical traffic conditions they rarely have to stop.

In the 1960s, experiments were made at the Holland Tunnel, one of the main arteries for traffic coming into and leaving New York City. When cars were allowed to enter the tunnel in the usual way, with no restrictions, the two-lane tunnel could handle 1,176 cars per hour, at an optimal speed of 19 miles per hour. But in a trial, the tunnel authorities capped the number of cars that could enter the tunnel every two minutes to 44. If that many cars got in before two minutes were up, a police officer made the next group of cars wait ten seconds at the tunnel entrance. The result? The tunnel now handled 1,320 vehicles per hour. (I will explain why shortly.) On streets with traffic signals, engineers set progressions with a certain speed in mind that will enable the driver to hit a line of constant greens. To drive faster than this only ensures that the driver will be forced to come to a stop at the next red light. Each stop requires deceleration and, more important, acceleration, which costs the driver in time and fuel. A queue of drivers stopped at a light is a gathering of "start-up lost time," as engineers call it (in an appropriately forlorn echo of Proust). The first cars in a queue squander an average of two seconds each, two seconds that would not have been lost had the car sailed through at the "saturation-flow" rate. The first driver at a light that turns from red to green, because he must react to the change, make sure that the intersection is empty, and accelerate from a standstill, generates the most "lost time." The light is green, but for a moment the intersection is empty. The second driver creates a bit less lost time, the third driver less still, and so on (a.s.suming everyone is reacting as soon as they can, which is not a given). SUVs, because they are longer (on average, 14 percent longer than cars), and take longer to accelerate, can create up to 20 percent more lost time.

Some of the start-up lost time could be "found" if drivers approached at a slower, more uniform speed that did not require them to come to a stop. (If they came too too slowly, however, time would also be lost, as green signal time would be wasted on an empty intersection.) Much of the time being lost these days is "clearance lost time," the time between signals when the intersection is momentarily empty. This is because traffic engineers are increasingly lengthening the "all-red phase," meaning that when one direction gets the red, the competing direction has to wait nearly two seconds before getting a green. They do this because more people cannot seem to stop on red. slowly, however, time would also be lost, as green signal time would be wasted on an empty intersection.) Much of the time being lost these days is "clearance lost time," the time between signals when the intersection is momentarily empty. This is because traffic engineers are increasingly lengthening the "all-red phase," meaning that when one direction gets the red, the competing direction has to wait nearly two seconds before getting a green. They do this because more people cannot seem to stop on red.

Now picture a highway during stop-and-go traffic. Like those drivers stopped at the light, each time we stop and start in a jam we are generating lost time. Unsure of what the drivers ahead are doing, we move in an unsteady way. We are distracted for a moment and do not accelerate. Or we overreact to brake lights, stopping harder than we need to and losing more time. Drivers talking on cell phones may lose still more time through delayed reactions and slower speeds. The closer the vehicles are packed together, the more they affect one another. Everything becomes more unstable. "All of the excess ability for the system to take in any sort of disturbance is gone," says Coifman. He uses the metaphor of five croquet b.a.l.l.s. "If you put them a foot apart and tap one lightly, nothing happens to the other four. If you put them all up against one another and tap one lightly, the far one then moves out. When you get closer to capacity on the roadway, if there's any one little tweak, it impacts a lot of the cars."

When the first in a group of closely s.p.a.ced cars slows or stops, a "shock wave" is triggered that moves backward. The first car slows or stops, and the next one slows or stops a little farther back. This wave, whose speed usually seems to register at about 12 miles per hour, could theoretically go on for as long as there was a string of sufficiently dense traffic. Even a single car on a two-lane highway, by simply changing its speed with little rhyme or reason (as people so often seem to do, in what I like to call "speed-attention-deficit disorder"), can itself pump these waves back down a stream of following vehicles. Furthermore, even if that car's average speed is fairly high, the fluctuations wreak progressive havoc. This was the secret behind the Holland Tunnel experiment: With cars limited to "platoons" of forty-four vehicles each, the shock waves that were triggered were confined to each group. The platoons were like croquet b.a.l.l.s s.p.a.ced apart.

Many times we find ourselves stuck in traffic that seems to have no visible cause. Or we make it through a jam and begin to speed up, seeming to make progress, only to quickly drive into another jam. "Phantom jams," these have been called, to the annoyance of some. "Phantom jams are in reality nonexistent," thunders Michael Schreckenberg, a German physics professor at the University of Duisburg-Essen so noted for his traffic studies that he has acquired the epithet "jam professor" in the German media. There is always a reason for a jam, he says, even if it is not apparent. What seems to be a local disturbance might just be a wave pumped up from downstream in what is in reality a big, wide moving jam. It is wrong, says Schreckenberg, to simply call the whole thing stop-and-go traffic: "Stop-and-go is the dynamic within within a jam." a jam."

We fall for the phantom-jam illusion because traffic happens in both time and s.p.a.ce. You may be driving into a s.p.a.ce where a jam has been. Or you may not be driving into a jam-instead, the jam might be driving into you. "In my bucket a.n.a.logy," says Coifman, "the driver would be a water molecule. If the water level's rising, then the jam's coming to us." We are also driving into history-or, perhaps more accurately, we are being driven back into history. By the time we actually arrive where something triggered the shock wave, in all likelihood the event will be only a memory. It may have been an accident, now cleared. "The queue's going to persist for a while as it's dissipating," says Coifman. "It's that water sitting in the bucket. In this case you've enlarged the hole in the bucket, but it does not disappear instantaneously."

Or the hiccup in heavy traffic that pa.s.ses through you might be the echo of someone who, forward in s.p.a.ce and backward in time, did something as simple as change lanes. The car that changes lanes moves, eating up capacity in the new lane and causing the driver behind to slow; it also frees up capacity in the lane it has left, which triggers a bit of acceleration in that lane. These actions ripple backward in a kind of seesaw effect. This is why, if you pick one car in the neighboring lane as your benchmark, you will often find yourself pa.s.sing that car and being pa.s.sed by that car continuously. This is equilibrium a.s.serting itself, the accordion of traffic flow stretching and compressing, the lingering chain reaction of everyone who thought they could get a better deal.

Since it takes so long for traffic to resume flowing freely once it has plunged past the critical density, it would seem the best way to avoid the ill effects of a jam would be not to drive into it, or let it drive into you, in the first place. This is the thought that occurred one afternoon a few years ago to Bill Beatty, a self-described "amateur traffic physicist" who works in the physics laboratory at the University of Was.h.i.+ngton. Beatty was on State Highway 202, returning from a state fair. The road, a "little four-lane," was thronged with traffic from the fair. The traffic was "completely periodic," as he describes it. "You'd drive real fast and then almost get to sixty and then you'd slow down and come to a stop, for almost two minutes," he says.

So Beatty decided to try an experiment: He would drive only 35 miles per hour. Rather than let the waves drive into him, he would "eat the waves," or subdue the wildly varying oscillations of stop-and-go traffic. Instead of tailgating and constantly braking, he would try to drive at a uniform speed, leaving a large gap between himself and the car ahead. When he looked in his rearview mirror, he saw a revelation in the pattern of headlights: Those behind him looked to be in a regular pattern, while the other lane had cl.u.s.ters of clumped stop-and-go vehicles. He had "damped" the wave, leveled off the extremes. "It cuts off the mountains and puts them in the valley," he says of his technique. "So instead of getting to drive at sixty miles per hour briefly, you're forced to drive at thirty-five miles per hour. But you don't have to stop, either."

Without a.n.a.lyzing the total traffic flow of the highway, it would be hard to know for sure what good Beatty's experiment did. People may have just merged in front of him, pus.h.i.+ng him back (if he wanted to keep the same following distance), while those behind him who thought he was going too slow may have jumped into the next lane, causing additional disturbance. But even if Beatty's technique did little more than take a tightly congested traffic jam and stretch it backward, so that a car spent the same amount of time traveling a section of road, it would still save fuel and reduce the risk of rear-end accidents-two added benefits for the same price. Only how do you get everyone to cooperate? How do you prevent people, as so often seems to happen, from simply consuming the s.p.a.ce you have left open? How, in essence, can we simulate ant-trail behavior on the highway?

One way is the "variable speed limit" system now being used on any number of roads, from England's M25 "controlled motorway" to sections of the German autobahn to the Western Ring Road in Melbourne, Australia. These systems link loop detectors in the road to changeable speed-limit signs. When the system notices that traffic has slowed, it sends an alert upstream. The approaching drivers are given a mandatory speed limit (enforced by license-plate cameras) that should, in theory, lessen the effects of a shock wave. Even though many drivers suspected it was the lowering of speeds to 40 kilometers per hour that was causing causing the congestion, a study of the M25 found that drivers spent less time in stop-and-go traffic, which not only helped lower the crash rate by 20 percent (itself good for traffic flow) but cut vehicle emissions by nearly 10 percent. As drivers adjusted to the system, their trip times declined. Again, slower can be faster. the congestion, a study of the M25 found that drivers spent less time in stop-and-go traffic, which not only helped lower the crash rate by 20 percent (itself good for traffic flow) but cut vehicle emissions by nearly 10 percent. As drivers adjusted to the system, their trip times declined. Again, slower can be faster.

Smart highways also require smart drivers. The sad truth is that the way we drive is responsible for a good part of our traffic problems. We accelerate too slowly or brake too quickly, or the opposite; since we do not leave enough s.p.a.ce between vehicles, the effects are often magnified as they move back up the line. Traffic is what is known as a nonlinear system, meaning most simply a system whose output cannot be reliably predicted from its input. When the first car in a long platoon comes to a stop, one cannot exactly predict how quickly or how far back each car behind it will stop (if they come to a stop at all). And the farther back, the harder it is to predict.

A driver's overreaction (or underreaction) may amplify a shock wave that snaps, like the crack of a whip, several cars back, helping to cause a collision in the s.p.a.ce that the originating driver has since left. One study examined a crash on a Minneapolis highway involving a platoon of seven vehicles that had been forced to come to a sudden stop. The seventh car in the group crashed into the sixth. Since we normally a.s.sume that cars keeping an adequate following distance should be able to stop in all conditions, that should be the end of it.

But the researchers, examining the braking trajectories of the vehicles in the platoon, found that the third third car arguably bore a considerable responsibility for the crash. How so? Because the third car was overly slow to react, it "consumed" a larger portion of the "shared resource" of braking distance allocated among the cars. This left the cars farther down the line with progressively less time and s.p.a.ce in which to stop-to the point where the seventh car, even though it reacted faster than the third, was following too closely to the sixth car to stop under the amplified conditions. Had the third car's reaction been faster, the crash might have been prevented. For these sorts of reasons, the researchers pointed out, people who tailgate-that is, do not follow at the "socially optimal" distance-increase their risk not only of striking the vehicle they're following but of being struck car arguably bore a considerable responsibility for the crash. How so? Because the third car was overly slow to react, it "consumed" a larger portion of the "shared resource" of braking distance allocated among the cars. This left the cars farther down the line with progressively less time and s.p.a.ce in which to stop-to the point where the seventh car, even though it reacted faster than the third, was following too closely to the sixth car to stop under the amplified conditions. Had the third car's reaction been faster, the crash might have been prevented. For these sorts of reasons, the researchers pointed out, people who tailgate-that is, do not follow at the "socially optimal" distance-increase their risk not only of striking the vehicle they're following but of being struck by the car following them. by the car following them.

What if drivers' reaction times could be predicted with mathematical precision? The ultimate answer may be to combine smart highways with smart cars. It's probably no accident that whenever one hears of a smart technology, it refers to something that has been taken out of human control. L. Craig Davis, a retired physicist who worked for many years in the research laboratories of the Ford Motor Company, is one of a number of people who have run simulations showing how equipping cars with adaptive cruise control (ACC), already found on many high-end models, can improve traffic flow by keeping the distance between cars at varying speeds mathematically perfect. This would not kill traffic waves entirely, says Davis. Even if a line of stopped cars could be coordinated to begin accelerating at the same time, he says, "if you wanted to get them up to speed with a normal distance between them at sixty miles per hour, you would still have this wave effect."

Remarkably, the simulations show that if just one in ten drivers had ACC, a jam could be made much less worse; with as few as two in ten drivers, the jam could be avoided altogether. could be avoided altogether. In one experiment, Davis located the precise moment the jam was avoided, just as one additional manual car was given ACC. This putative straw that broke the camel's back brings to mind the example of the locusts. When the locusts reached critical density-one more locust-they began to behave entirely differently. In one experiment, Davis located the precise moment the jam was avoided, just as one additional manual car was given ACC. This putative straw that broke the camel's back brings to mind the example of the locusts. When the locusts reached critical density-one more locust-they began to behave entirely differently.

Just one problem has arisen in Davis's simulations. Since the simulated vehicles with ACC like to keep very tight gaps between themselves, it may be difficult for a non-ACC car entering from an on-ramp to find a safe s.p.a.ce between them. Also, like human drivers, ACC cars may not feel obliged to yield to entering drivers. These problems can surely be solved scientifically, but in the meantime, as we suffer the effects of our failure to always act cooperatively on the highway, we can draw one comforting lesson: Even machines sometimes have trouble merging.

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Why Women Cause More Congestion Than Men (and Other Secrets of Traffic) Who Are All These People? The Psychology of Commuting You're not stuck in a traffic jam. You are the traffic jam.

-advertis.e.m.e.nt in Germany

One of the curious laws of traffic is that most people, the world over, spend roughly the same amount of time each day getting to where they need to go. Whether the setting is an African village or an American city, the daily round-trip commute clocks in at about 1.1 hours.

In the 1970s, Yacov Zahavi, an Israeli economist working for the World Bank, introduced a theory he called the "travel-time budget." He suggested that people were willing to devote a certain part of each day to moving around. Interestingly, Zahavi found that this time was "practically the same" in all kinds of different locations. The small English city of Kingston-upon-Hull's physical area was only 4.4 percent the size of London; nevertheless, Zahavi found, car drivers in both places averaged three-quarters of an hour each day. The only difference was that London drivers made fewer, longer trips, while Kingston-upon-Hull drivers made more frequent, shorter trips. In any case, the time spent driving was about the same.

The noted Italian physicist Cesare Marchetti has taken this idea one step further and pointed out that throughout history, well before the car, humans have sought to keep their commute at about one hour. This "cave instinct," as he calls it, reflects a balance between our desires for mobility (the more territory, the more resources one can acquire, the more mates one can meet, etc.) and domesticity (we tend to feel safer and more comfortable at home than on the road). Even prisoners with life sentences, he notes, get an hour "out in the yard." When walking was our only commuting option, an average walking speed of 5 kilometers per hour meant that the daily commute to and from the cave would allow one to cover an area of roughly 7 square miles (or 20 square kilometers). This, remarks Marchetti, is exactly exactly the mean area of Greek villages to this day. Moreover, Marchetti notes, none of the ancient city walls, from Rome to Persepolis, encompa.s.sed a s.p.a.ce wider than 5 kilometers in diameter-in other words, just the right size so that one could walk from the edge of town to the center and back in one hour. Today, the old core of a pedestrian city like Venice still has a diameter of 5 kilometers. the mean area of Greek villages to this day. Moreover, Marchetti notes, none of the ancient city walls, from Rome to Persepolis, encompa.s.sed a s.p.a.ce wider than 5 kilometers in diameter-in other words, just the right size so that one could walk from the edge of town to the center and back in one hour. Today, the old core of a pedestrian city like Venice still has a diameter of 5 kilometers.

The growth of cities was marked, like tree rings, by advances in the ways we had to get from one place to another. The Berlin of 1800, Marchetti points out, was a walkable size. But as horse trams came along, then electric trams, then subways, and, finally, the car, the city kept growing, by roughly an amount proportional to the speed increase of the new commuting technology-but always such that the center of the city was, roughly, thirty minutes away for most people.

The "one-hour rule" found in ancient Rome still exists in modern America (and most other places), even if we have swapped sandals for cars or subways. "The thing to recognize is that half the U.S. population still gets to work in almost twenty minutes, or under twenty minutes," says Alan Pisarski, the country's leading authority in the field of "travel behavior." For decades, Pisarski has been compiling numbers for the U.S. Census on how we get to work and how long that trip takes us. There seems to be some innate human limit for travel-which makes sense, after all, if one sleeps eight hours, works eight hours, spends a few hours eating (and not in the car), and crams in a hobby or a child's tap-dance recital. Not much time is left. Studies have shown that satisfaction with one's commute begins to drop off at around thirty minutes each way.

The enduring persistence of the one-hour rule was shown in a paper by urban planning researchers David Levinson and Ajay k.u.mar. Looking at the Was.h.i.+ngton, D.C., metropolitan area over a number of years from the 1950s to the 1980s, they found that average travel times-around thirty-two minutes each way-had hardly budged across the decades. What had had changed were two other factors: distance and average travel speed. Both had gone up. They suggested that people were acting as "rational locators." Because they did not want to spend too long commuting, they had moved to more distant suburbs. They had longer distances to drive, but they could now travel on faster suburban roads, rather than crowded city streets, to get to where their jobs were located. (Those in the center city, meanwhile, were probably walking to work or taking the Metro, meaning their times had hardly changed as well.) changed were two other factors: distance and average travel speed. Both had gone up. They suggested that people were acting as "rational locators." Because they did not want to spend too long commuting, they had moved to more distant suburbs. They had longer distances to drive, but they could now travel on faster suburban roads, rather than crowded city streets, to get to where their jobs were located. (Those in the center city, meanwhile, were probably walking to work or taking the Metro, meaning their times had hardly changed as well.) "Wait," I can hear you say, "I thought traffic was getting worse." For many people, it undoubtedly is. The Texas Transportation Inst.i.tute estimates that total traffic delay in the United States went from 0.7 billion hours in 1982 to 3.7 billion hours in 2003. In the twenty-six largest urban areas, the delay grew almost 655 percent in those same years. The U.S. Census noted that in most large cities, it took longer to get to work in 2000 than it did in 1990. The authors of the "rational locator" study took another look at the issue and decided that perhaps travel times were not not stable after all. Perhaps, they suggested, it was a "statistical artifact." Cities were growing larger every year, gobbling up new counties into their "metropolitan region," so maybe more-distant drivers who were not tallied in previous surveys were now being captured, jacking up the numbers. Or maybe the suburbs that they had moved to previously to escape congestion were now themselves getting congested. Perhaps the total outcome of all that rational location had itself become irrational. stable after all. Perhaps, they suggested, it was a "statistical artifact." Cities were growing larger every year, gobbling up new counties into their "metropolitan region," so maybe more-distant drivers who were not tallied in previous surveys were now being captured, jacking up the numbers. Or maybe the suburbs that they had moved to previously to escape congestion were now themselves getting congested. Perhaps the total outcome of all that rational location had itself become irrational.

But why exactly is it getting worse? Or, to ask a question I sometimes do when I encounter unexpectedly heavy congestion in the middle of the day, "Who are all these people?" There are obvious answers, the ones you yourself suspect, like the fact that we add new drivers faster than we keep adding new blacktop. To take a quite typical American example: In suburban Montgomery County, Maryland, just outside Was.h.i.+ngton, D.C., the population grew by some 7 percent between 1976 and 1985. The number of jobs grew too, by 20 percent. But vehicle registrations nearly doubled. The county, which hardly built any new roads at all during that period, was suddenly awash in cars. Studies show that when a household has more vehicles, it not only drives more as a total household, as one would expect, but each person each person puts on more miles, almost as if the presence of those extra vehicles prompts more driving. puts on more miles, almost as if the presence of those extra vehicles prompts more driving.

Affluence breeds traffic. Or, as Alan Pisarski describes it, congestion is "people with the economic means to act on their social and economic interests getting in the way of other people with the means to act on theirs." The more money people have, the more cars they own, the more they drive (with the exception of a few Manhattan millionaires). The better the economy, the more miles traveled, the worse the traffic congestion. This is the interesting thing about studying traffic behavior: It reveals what Pisarski terms our "lines of desire." The U.S. Census is like a staid group portrait of the country. It shows us all in our homes, with our 2.3 bathrooms and 1.3 cats. But it does not really show us how we got there. The travel census is like a frantic, blurred snapshot of a nation in motion. It catches us on the move, in an unrehea.r.s.ed moment, busily going about our daily lives in order to afford that house with 2.3 bathrooms. It may tell us more about ourselves than we know.

One striking thing the numbers seem to reveal is that women now make the largest contribution to congestion. (Another way to look at this is that they also suffer from it the most.) This seems like a controversial statement, and indeed one like it got a highway official booed at a conference. The statistic doesn't a.s.sign fault or suggest that women working is a bad thing; it does provide a fascinating example of how traffic patterns are not just anonymous flows in the models of engineers, but moving, breathing time lines of social change.

Many of us can remember or envision a time when the typical commute involved Dad driving to the office while Mom took care of the kids and ran errands around town. Or, because many American families had only one car, Dad was driven to the morning train and picked up again just in time for c.o.c.ktail hour and Cronkite. This is a blinkered view, argues Sandra Rosenbloom, an urban planning professor at Arizona State University whose specialty is women's travel behavior. "That was just a middle-cla.s.s model," she says. "Lower-cla.s.s women always worked. Either alongside husbands in stores, or at home doing piecework. Women always worked."

Still, the Leave It to Beaver Leave It to Beaver commute was not a total fiction, given that in 1950 women made up 28 percent of the workforce. Today, that figure is 48 percent. How could the roads commute was not a total fiction, given that in 1950 women made up 28 percent of the workforce. Today, that figure is 48 percent. How could the roads not not have gotten more crowded? "The rise in the number of cars, driver's licenses, miles traveled-it totally tracks women going into the labor force," says Rosenbloom. "It's not that men wouldn't have driven more, but you wouldn't see these astonis.h.i.+ng increases in traffic congestion in all indices of travel if women weren't in the labor force, driving." have gotten more crowded? "The rise in the number of cars, driver's licenses, miles traveled-it totally tracks women going into the labor force," says Rosenbloom. "It's not that men wouldn't have driven more, but you wouldn't see these astonis.h.i.+ng increases in traffic congestion in all indices of travel if women weren't in the labor force, driving."

The rise in working women is only part of the story. After all, they still represent a minority of the workforce, and studies show that men still rack up more miles when they drive to work. But work is an increasingly small part of the picture. In the 1950s, studies revealed that about 40 percent of daily trips per capita were "work trips." Now the nationwide figure is roughly 16 percent. It's not that people are making fewer trips to work but that they're making so many other kinds of trips. What kinds of trips? Taking the kids to school or day care or soccer practice, eating out, picking up dry cleaning. In 1960, the average American drove 20.64 miles a day. By 2001, that figure was over 32 miles.

Who's making these trips? Mostly women. This is the kind of social reality that traffic patterns lay on the table: Even though women make up nearly half the workforce, and their commutes are growing increasingly close in time and distance to men's, they're still doing a larger share of the household activities that, back in the Leave It to Beaver Leave It to Beaver days, they may have had the whole day to complete (and, as Rosenbloom points out, 85 percent of single parents are women). "If you look at trip rates by male versus female, and look at that by size of family," Pisarski says, "the women's trip rates vary tremendously by size of family. Men's trip rates look as if they didn't even know they days, they may have had the whole day to complete (and, as Rosenbloom points out, 85 percent of single parents are women). "If you look at trip rates by male versus female, and look at that by size of family," Pisarski says, "the women's trip rates vary tremendously by size of family. Men's trip rates look as if they didn't even know they had had a family. The men's trip rates are almost independent of family size. What it obviously says is that the mother's the one doing all the hauling." a family. The men's trip rates are almost independent of family size. What it obviously says is that the mother's the one doing all the hauling."

In fact, women make roughly double the number of what are called "serve-pa.s.senger" trips-that is, they're taking someone somewhere that they themselves do not need to be. All these trips are squeezed together to and from work in a process called "trip chaining." And because women, as a whole, leave later for work than men, they tend to travel right smack-dab in the peak hours of congestion (and even more so in the afternoon peak hours, which is partially why those tend to be worse). What's more, these kinds of trips are made on the kinds of local streets, with lots of signals and required turning movements, that are least equipped to handle heavy traffic flows.

Another way trip chaining has helped increase traffic congestion is that it has made carpooling virtually impossible. Who wants to share a ride with someone who is going to day care, picking up laundry, dropping by Blockbuster, stopping at Aunt Clarice's ("but just for a second")? Carpooling keeps dropping in the United States (save among some immigrant groups), but "fam-pools," car pools made up of family members (and almost 100 percent of fam-pools are only only family members), keep rising. An estimated 83 percent of car pools are now fam-pools. family members), keep rising. An estimated 83 percent of car pools are now fam-pools.

This raises the question of whether car-pool lanes are a good idea that has gone bad. If most people "carpooling" are simply toting their families around, taking no additional cars off the road and statistically driving more miles (thus creating more traffic), why should they get a break on the highway? Is a policy meant to reduce the number of drivers just acting as a "mommy lane," enabling drivers with children to do their trip chaining more quickly and thus encouraging more of it? (Some pregnant women have taken this to extremes, arguing that their unborn children are precocious car poolers).

That women suffer more from congestion, even if at the hands of other women, is demonstrated in the high-occupancy toll lanes (HOT lanes, a.k.a. Lexus lanes) in cities like Denver, where drivers pay more to travel on less congested roads. Rosenbloom notes that studies show that women pay to use the lanes more often than men do-despite making less money on average. "And they are not just high-income women," she says. "Even if you don't make very much money, you've got to get your kids from day care. Every minute they stay over, they penalize you. Or these women have second jobs they have to get to on time."

Women are not to be blamed blamed for congestion, Rosenbloom argues. "The fault is the way families live today. The car is the way the two-worker families balance all the things they have to do." Where children might once have been cared for at home, they are now shuttled to day care. Where it was once the overwhelming norm for children to walk to school, today only about 15 percent do. Parents on the "school run" are thought to boost traffic on the roads by some 30 percent. for congestion, Rosenbloom argues. "The fault is the way families live today. The car is the way the two-worker families balance all the things they have to do." Where children might once have been cared for at home, they are now shuttled to day care. Where it was once the overwhelming norm for children to walk to school, today only about 15 percent do. Parents on the "school run" are thought to boost traffic on the roads by some 30 percent.

Parents' chauffeuring duties hardly end there, however, as the increasingly hyperscheduled "free time" of children, with its scores of games, lessons, and playdates, requires route planning and logistics that would turn a La Guardia air-traffic controller's hair gray. It's estimated that from 1981 to 1997, the amount of time children spent in organized sports in America doubled. doubled. All those games and all those practices, in increasingly far-flung suburbs, required rides. A new demographic ent.i.ty, the so-called soccer mom, started hitting the roads big-time. "In the entire time I played baseball, my parents didn't watch me play ball once," recalls Pisarski, who is in his sixties. "I didn't feel slighted, because no other kid's parents were there either. Today you go to a game, and there's a hundred and fifty people and everybody gets a trophy." All those games and all those practices, in increasingly far-flung suburbs, required rides. A new demographic ent.i.ty, the so-called soccer mom, started hitting the roads big-time. "In the entire time I played baseball, my parents didn't watch me play ball once," recalls Pisarski, who is in his sixties. "I didn't feel slighted, because no other kid's parents were there either. Today you go to a game, and there's a hundred and fifty people and everybody gets a trophy."

Traffic, Pisarski emphasizes, is the expression of human purpose. Another huge way in which those purposes have changed is due to rising affluence. It's not just that American households have more cars, it is that they are finding new places to take them. And once you have sh.e.l.led out for a car, the comparatively marginal cost of another trip is barely noticeable-in other words, there is little incentive not not to drive. to drive.

Given that Americans increasingly spend much of what they make, it should come as little surprise that much of our increase in driving seems to stem from trips to the mall. From 1983 to 2001, the number of annual shopping trips per household almost doubled doubled-and those trips are getting longer. Each year, the amount of driving we do for shopping would take us across the country once and almost all the way back again. Statistics now show that more people travel on Sat.u.r.day at one p.m. than during the typical rush hours. The more money one has, the more choices one has, and so it's not surprising that nearly half of trips families make to supermarkets are not to those closest to their home. Pisarski notes that he, like many Americans, does not suffer for choice when it comes to food shopping, and his driving reflects this. "I go to Trader Joe's because I like their string beans. I go to Harris Teeter because their seafood is better than Giant. In effect, we are just more selective." Studies confirm that people shop at more grocery stores than they did a few decades ago.

You might think that the rise of larger, consolidated stores like Costco or Wal-Mart Supercenters, which offer one-stop shopping, might have actually helped cut down on the amount of shopping trips. But larger stores need to serve more people, which means, in effect, that they're farther away from more people. (A similar trend has also occurred with schools, which explains some of the decline in children's walking.) A study of Seattle grocery stores found that in 1940, the average store was .46 miles from a person's house, while in 1990, it was .79 miles. That small change in distance was basically the death knell for any thought of not not driving to the store, for a half mile is as long as planners believe the average person is willing to walk. Even if the stores are bigger, moreover, we are going to them more frequently-the number of grocery trips per week almost doubled from the 1970s to the 1990s. driving to the store, for a half mile is as long as planners believe the average person is willing to walk. Even if the stores are bigger, moreover, we are going to them more frequently-the number of grocery trips per week almost doubled from the 1970s to the 1990s.

The reason we see so many people on the roads, getting in our way, is that so many of them are doing things that used to be done at home. This, too, is a function of affluence, but it's a complicated relations.h.i.+p. Do we drive to a restaurant for take-out food because we can afford it or because we are so busy trying to make money we have little choice? Either way, these sorts of social changes have their effects on traffic-often so fast that engineers can't keep up. When Starbucks began serving customers at drive-throughs a few years ago, the people who study traffic flows were caught flat-footed. Their models for what is called "trip generation"-basically, the additional traffic flow a new business will create-included numbers for "Fast Food Restaurants with Drive-Through Window," as well as for "Coffee/Bread/Sandwich Shop," but "Coffee Place with Drive-Through Window" was completely alien. For Starbucks, which will go so far as to put stores on opposing corners to capture different traffic flows and spare drivers the agony of having to make a left turn during rush hour, the drive-through represented a natural progression in its slow evolutionary insertion into the daily commute.

"Can you imagine, thirty years ago, saying n.o.body will make coffee at home?" Nancy McGuckin, a travel researcher in Was.h.i.+ngton, D.C., asked me on a break during an annual traffic conference. In her research, McGuckin (whom one colleague called "the queen of trip chaining") fingered coffee as a prime culprit in a dramatic new s.h.i.+ft in traffic patterns. Men, it seemed, were suddenly doing more trip chaining. Sure, some some were dropping off kids, but more were making a latte stop. She calls this the "Starbucks effect." The prime demographic, she says, is middle-aged men. "Who knew they needed 'me time'?" she asks. "We're used to women saying this: 'We're so busy, we need "me time."' But it was middle-aged men who were making that stop at Starbucks in the morning. I had some of them saying they were leaving their homes before it becomes chaotic with the backpacks and the school. [He wants] to get up and leave the house and go to Starbucks, where, by golly, there's somebody there who greets him by name, knows what his favorite drink is. It's like his time to prepare for the office environment. I don't think the psychology of that has been explored very well." were dropping off kids, but more were making a latte stop. She calls this the "Starbucks effect." The prime demographic, she says, is middle-aged men. "Who knew they needed 'me time'?" she asks. "We're used to women saying this: 'We're so busy, we need "me time."' But it was middle-aged men who were making that stop at Starbucks in the morning. I had some of them saying they were leaving their homes before it becomes chaotic with the backpacks and the school. [He wants] to get up and leave the house and go to Starbucks, where, by golly, there's somebody there who greets him by name, knows what his favorite drink is. It's like his time to prepare for the office environment. I don't think the psychology of that has been explored very well."

The same might be said for the psychology of commuting itself. It does not seem unreasonable to wonder why, if traffic is so bad, more people keep choosing to drive more miles. This question puzzles all kinds of people, from economists to psychologists to traffic engineers.

One important thing to consi