But they have one big drawback: The on-ramp loop enters the highway just beyond where cars are exiting via the off-ramp loop. The two streams must mix. Engineers call this the “weaving section,” a mysterious, traffic-tossed tempest full of what engineers call “turbulence” and “friction,” in which people coming onto and getting off the highway end up in each other’s way. Drivers at different speeds, scanning for directional signs, have to probe openings (i.e. make “gap acceptance” decisions) and sometimes get across several lanes—often quite suddenly. Interchanges, as it happens, are where most crashes on freeways occur—according to studies, the shorter the weave section, the higher the crash rate. With light traffic, the cloverleaf presents less of a problem, but when “weaving volume” on the two loops tops the magic number of one thousand vehicles per hour (hardly a rarity these days), things begin to break down. Because of the curious nonlinear dynamics of traffic, when traffic volume doubles, the length of weaving section required to keep it moving smoothly triples. Over time, engineers have responded by moving the weaving section out of the main highway flow and onto special “collector” lanes, which, where possible, seems to be safer and more efficient.
Highways are continuing to evolve. Recently, as traffic volumes have grown, and with new highway building increasingly unaffordable or undesirable, some agencies have begun adding new lanes to highways by either eliminating the shoulder lane or making the existing lanes narrower. In theory, this is riskier because on narrow lanes there is a greater chance of one car drifting into another. There is literally less room for error. On the other hand, wider lanes, which are presumably safer, have been shown to increase speed and may encourage drivers to drive less cautiously. Indeed, some reports have even suggested that lanes wider than the typical U.S. twelve-foot standard may actually be less safe. So far, studies that have looked into the narrowing of highway lanes have come to mixed conclusions on whether the new layouts are more or less safe. In some cases, the difference was not statistically significant. This suggests that the way drivers behave is as important as the way a road is designed. As Ezra Hauer, a Canadian engineer and traffic-safety expert, once put it, “Drivers adapt to the road they see.”
There is a simple mantra you can carry about with you in traffic: When a situation feels dangerous to you, it’s probably more safe than you know; when a situation feels safe, that is precisely when you should feel on guard. Most crashes, after all, happen on dry roads, on clear, sunny days, to sober drivers.
The Trouble with Traffic Signs—and How Getting Rid of Them Can Make Things Better for Everyone
Try to remember the last time you saw, while driving, a “School Zone” or “Children at Play” sign. Chances are you will not remember, but if you can, now try to recall what you did when you saw it. Did you suddenly slow? Did you scan for children? If you’re like most people, you did nothing. You may not have understood what it was asking you to do, which is rather common—in one study, subjects who were shown a sign warning, WATCH FOR FALLEN ROCKS, were split equally between those who said they would look for rocks falling at the moment and speed up and those who said they would slow down and look for rocks already on the road. Perhaps signs should simply say, WATCH FOR ALL ROCKS, EVERYWHERE.
More likely, the reason you did nothing when you saw the sign is that there were no children playing. If there were children playing, you probably saw them before you saw the sign. “Children at Play” signs have not been shown to reduce speeds or accidents, and most traffic departments will not put them up. Yet why do we seem to see so many? City governments usually post them to assuage complaints by neighborhood residents that people are speeding down their streets. They may have even been put up after a child was hit or killed by a driver, in which case it would probably be more effective to erect a sign saying just that.
Similarly, drivers routinely see signs warning of deer crossings (in the United States) or elephant crossings (in Sri Lanka) or camel crossings (in Tunisia). It is difficult to say what’s going on in the mind of a driver when he or she sees a deer or elephant or camel crossing sign, but studies have shown that most drivers do not change their speed at all. A Colorado trial featured a special animated deer sign (no, it wasn’t Bambi). Researchers presumed that the animated sign would draw more attention and heighten driver awareness. For a few weeks, it was turned away from the road, then turned back. There were actually more deer killed when the sign was activated than when it was not, even though fewer deer had crossed. The researchers then went so far as to place a deer carcass next to the animated sign—only then did drivers finally slow.
Traffic engineers have tried putting signs up only during migratory seasons or using special flashing signs equipped with sensors to detect the presence of deer, but these so-called dynamic signs are not only costly but prone to false alarms and maintenance issues, not to mention being riddled with buckshot, particularly in parts of rural America. (Maybe in the off-season deer hunters practice on deer signs.) Researchers in Wyoming who put up a special deer-sensing, flashing system were able to get some drivers to slow down when they included a deer decoy, but they walked away with the opinion that “these reductions in vehicle speed would most likely not reduce the probability of a deer-vehicle collision.” Maybe deer should simply be dressed in head-to-toe blaze orange outfits, like the people hunting them!
Perhaps the most absurd warning-sign case involved moose advisories in Newfoundland. One foggy stretch of road was home to not only many car-moose collisions but many collisions between cars and cars stopping to take pictures of moose. And so signs were erected that featured full-size, reflective silhouettes of moose. Unfortunately, tourists found these pretty interesting too, and as they slowed or stopped to take photos, the moose signs themselves became crash hot spots. The next logical step? Create new signs that read CAUTION: MOOSE SIGNS AHEAD.
Many traffic signs have become like placebos, giving false comfort to the afflicted, or simple boilerplate to ward off lawsuits, the roadway version of the Kellogg’s Pop-Tarts box that says, “Warning: Pastry Filling May Be Hot When Heated.” Engineers insist that they are necessary to protect municipalities from liability lawsuits.
But what is a sign actually telling a driver? As Carl Andersen of the FHWA pointed out during my visit, the same sign can mean two different things in two different places. Take the chevron warning sign, the one that looks like a mathematical “greater or less than” symbol. “You drive in Vermont and you see a chevron sign, you better start braking for that curve,” Andersen said. “You see that chevron in Connecticut, you better ignore it. They pick different rates of curvature to put these chevron signs up to provide that kind of warning. So even though there’s guidelines to do it consistently, there’s enough leeway in there that they do it at different times.” Nor does a sign always mean the same thing: “Bridge Freezes Before Roadway” does not tell the driver whether the bridge is frozen, and in July it tells the driver absolutely nothing. Should a “65 MPH” speed-limit sign say something else when it’s raining? Engineers have created costly dynamic signs in response to all of these issues, but the real question may be, At what point must common sense do the work of a sign?
If “Slow: Children” and “Deer Crossing” signs do not seem to have noticeable effects, it hardly seems impertinent to ask, Do traffic signs work, and are they really needed at all? This question has been raised by Hans Monderman, a pioneer who was, until his death in January 2008, perhaps the world’s best-known traffic engineer. It’s probably no accident that he became famous by turning his back on decades of received wisdom in his profession and created traffic plans—like entire major intersections without lights or signs—that were radical even by the standards of his native Holland. “The Netherlands is different,” noted Kerstin Lemke, a researcher at Germany’s Federal Highway Research Institute, as if discussing the openness toward sex and drugs in Amsterdam. “They’ve got things on the motorway we would never do.” Then again, the Netherlands has a be
tter traffic-safety record than Germany, so maybe they’re on to something.
If people have heard of Monderman, they tend to recall something about “the guy in the Netherlands who hated traffic signs.” But there is, in fact, one traffic sign that Monderman loved. It stands at the border of the small village of Makkinga, in Friesland. It announces a 30 kilometers per hour speed limit. Then it says, WELKOM. Finally, it says: VERKEERSBORDVRIJ!! In English this means, roughly, “Free of traffic signs.”
A traffic sign announcing the lack of traffic signs is a good joke, but it’s also a perfect symbol of Monderman’s philosophy. The sign itself is superfluous, for a driver can see that there are no traffic signs in Makkinga. After all, Monderman pointed out, what do traffic signs actually tell us? One day, driving through Friesland in his Volvo, Monderman gestured toward a sign, just before a bridge, that showed a symbol of a bridge. “Do you really think that no one would perceive there is a bridge over there?” he asked. “Why explain it? How foolish are we in always telling people how to behave. When you treat people like idiots, they’ll behave like that.”
Monderman’s work was far more complex than a simple dislike of traffic signs. It revolved around a central theory that said there are two kinds of space: The “traffic world” and the “social world.” The traffic world is best exemplified by the highway. This world is impersonal, standardized, meant only for cars. It is all about speed and efficiency and homogeneity. Monderman, a great fan of the German autobahn, happened to like this world. The social world, on the other hand, is seen in a place like a small Dutch village. These are places where the car is meant to be a guest, not the sole inhabitant. The street has other uses beyond being a means for people to drive quickly from one place to another. Behavior is governed by local customs and interpersonal contact more than abstract rules. Monderman liked this world too, but he did not want it to have anything in common with the German autobahn.
Yet the traffic engineers, argued Monderman, with their standardized signs and markings, have forced the traffic world upon the social world. “When you built a street in the past in our villages, you could read the street in the village as a good book,” he said. “It was as readable as a book. Here is the entrance to the village, over there is a school, maybe you can shop in that shop over there. There’s a big farmyard and perhaps there’s a tractor coming out. Then the traffic engineers came and they changed it into an absolute uniform piece of space.” Drivers, he maintained, are no longer taking cues from the social life of the village; they’re working off the signs, which have become such a part of our world that “we don’t see them anymore.” Suddenly, the village’s main road is just another segment of the highway passing through, with only a few small signs to tell anyone otherwise. This may be why speeding tickets are so common at the entrances to small towns all over the world. Rather than the simple greed of the local municipality, it is also that the road through the village so often feels the same as the road outside the village—the same width, the same shoulders. The speed limit has suddenly been cut in half, but the driver feels as if he or she is still driving the same road. That speeding ticket is cognitive dissonance.
In the mid-1980s, Monderman had an epiphany that is still reverberating throughout the world. He was called in to rework the main street of a village called Oudehaske. Villagers, as they do the world over, were complaining about cars speeding through the village, on a wide asphalt road with steady traffic volumes. Before Oudehaske, Monderman’s response, like that of any good Dutch traffic engineer, had been to deploy the arsenal of what is known as “traffic calming.”
Traffic calming is, essentially, the art of getting drivers to slow down. You have traveled down a street on which traffic-calming measures have been applied, even if you were not aware of the taxonomy of devices. The most famous is the speed bump, the steep, jarring obstruction that dates to the dawn of the car itself. With the exception of places like Mexico City, speed bumps are mostly restricted to school parking lots and the like. What you see on streets nowadays is the “speed hump,” a wider, more gently sloping creature that, among other things, helps cities avoid lawsuits from car owners with ruined suspensions. There are a veritable Audubon guide’s worth of different hump styles, from “parabolic” to “sinusoidal” to the popular English import known as the “Watts profile.” A really wide hump with a flat plateau is called a “speed table.” Apart from these myriad undulations, there are also “chicanes,” which sound like French cigarettes but are really little S-shaped artificial curves that drivers must slow to navigate. “Neck-downs” (a.k.a. “bulb-outs,” “nubs,” or “knuckles”), meanwhile, are small extensions added to curbs to make intersections narrower, meant to induce drivers to slow and, at the very least, give pedestrians a shorter—and thus safer—distance to cross.
The list goes on—which should give you an idea of how hard it is to calm traffic—with any number of “diagonal diverters,” “median chokers,” and “forced-turn islands” (also called “pork chops,” for their shape). If you want to sound smart around your friends, just remember that engineers refer to bumps and the like as “vertical deflection,” while anything that relies on squeezing and narrowing is “horizontal deflection.”
Traffic-calming devices have been shown to slow speeds and reduce the volume of through traffic. But as with any medicine, the right drug—and the right dosage—must be administered. Many people think that stop signs are a good way to calm speeds in neighborhoods. One problem is that the power of these signs diminishes with use: The more stop signs, the more likely drivers are to violate them. Studies have also shown that stop signs do little if anything to reduce speed—drivers simply go faster at the midblock location to make up time. This issue plagues speed humps too, which is why engineers advise placing them no more than three hundred feet apart, so drivers do not have time to speed. As with any drug, there are side effects: Slowing and accelerating for humps increases noise and emissions, while studies have suggested that speed humps on one block can lead to higher speeds or more traffic on another. People opposed to traffic-calming measures have argued that they delay emergency responders, but researchers in Portland, Oregon, found that they added ten seconds at most to these trips—no more than any other random delay. Would you want to live on a neighborhood street that made the rare fire-truck visit ten seconds faster but was also a safe haven for faster, noisier, and more dangerous traffic every day?
As it happens, many of these traffic-calming innovations were first popularized in the Netherlands. In the beginning, they were almost impromptu acts, a kind of radical street theater directed against the growing encroachment of cars in the city. Joost Váhl, a progressive engineer working for the city of Delft in the late 1960s, was one of their key architects. Sitting one afternoon in his tidy house in Culemborg, Váhl recalled a series of outlandish stunts that ranged from a “dial-a-bump” service (citizens could call and request “bumps” in front of their homes), to the staging of a bicycle accident (“we wanted to know if car drivers would stop and help or pass us by”), to putting up false construction sites on city streets (“we found out that when streets are broken up for repair, everything is functioning perfectly with half of the space”). These tactics, which were really investigations into how to get cars and people to coexist in cities, eventually made their way into genuine social institutions. The most famous of these were the woonerven—the word translates roughly into “living yards”—which began to spring up in European cities in the early 1970s.
For decades, planners had said that people and traffic should be segregated, with cars on speedy urban motorways and pedestrians shuttling around on elevated networks of bridges and walkways. Many saw this as a capitulation of the city to the car, while as early an observer as Charles Dickens understood the futility in trying to get pedestrians to ascend pedestrian bridges when people preferred to simply cross at street level. (“Most people would prefer to face the danger of the street,” he wrote, “rather than t
he fatigue of getting upstairs.”)
The woonerven reversed this idea, suggesting that it was people who lived in cities and that cars were merely guests. Neighborhood streets were “rooms” to be driven through, at no higher than walking speeds of 5 to 10 miles per hour, with drivers being mindful of the furniture and decor—not just speed humps but benches, flowerpots, and nice cobble-stones—and, more important, the residents. Even today, woonerven plans seem radical, with children’s sandboxes sitting cheek-by-jowl to the street and trees planted in the middle of traffic. The reports that trickled in, however, talked about how children were playing outside longer, often without supervision. In time, the woonerven got their own traffic signs (a small icon of a house with a child standing next to it). These were marks of the concept’s success, but in the eyes of Monderman, those signs also rather defeated the purpose: Drive carefully near the woonerven, the sign implies, but drive less carefully everywhere else.
By the time Monderman had been called to rework the village of Oudehaske, the political winds of traffic planning had shifted, and suddenly things like speed bumps were out of favor. In any case, Monderman did not have the budget for traffic-calming infrastructure. At a loss, he suggested that the road simply be made more “villagelike.” Maybe if the road looked more like a village road and less like the highway leading out of town, people would act accordingly. The village, coincidentally, had called in some consultants to redesign the village itself. Why not extend the treatment to the road? Working with the consultants, Monderman offered a design. “I thought, this must go wrong. There were no flowerpots, no chicanes. It was just a simple road in a village, nothing more.” A month after the project was finished, Monderman took a radar gun and measured the speed of cars passing through the village. In the past, with his chicanes and flowerpots, he would have been lucky to get a 10 percent drop in speed. This time, the speed had dropped so much that he could not get a reading. “The gun only functioned at thirty kilometers per hour,” he recalled.
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