Distracting Miss Daisy

Why stop signs and speed limits endanger Americans

There is a stretch of North Glebe Road, in Arlington, Virginia, that epitomizes the American approach to road safety. It’s a sloping curve, beginning on a four-lane divided highway and running down to Chain Bridge, on the Potomac River. Most drivers, absent a speed limit, would probably take the curve at 30 or 35 mph in good weather. But it has a 25-mph speed limit, vigorously enforced. As you approach the curve, a sign with flashing lights suggests slowing further, to 15 mph. A little later, another sign makes the same suggestion. Great! the neighborhood’s more cautious residents might think. »

We’re being protected. But I believe policies like this in fact make us all less safe.

I grew up in Great Britain, and over the past five years I’ve split my time between England and the United States. I’ve long found driving in the U.S. to be both annoying and boring. Annoying because of lots of unnecessary waits at stop signs and stoplights, and because of the need to obsess over speed when not waiting. Boring, scenery apart, because to avoid speeding tickets, I feel compelled to set the cruise control on long trips, driving at the same mind-numbing rate, regardless of road conditions.

Relatively recently—these things take a remarkably long time to sink in—I began to notice something else. Often when I return to the U.S. (usually to a suburban area in North Carolina’s Research Triangle), I see a fender bender or two within a few days. Yet I almost never see accidents in the U.K.

This surprised me, since the roads I drive here are generally wider, better marked, and less crowded than in the parts of England that I know best. And so I came to reflect on the mundane details of traffic-control policies in Great Britain and the United States. And I began to think that the American system of traffic control, with its many signs and stops, and with its specific rules tailored to every bend in the road, has had the unintended consequence of causing more accidents than it prevents. Paradoxically, almost every new sign put up in the U.S. probably makes drivers a little safer on the stretch of road it guards. But collectively, the forests of signs along American roadways, and the multitude of rules to look out for, are quite deadly.

Economists and ecologists sometimes speak of the “tragedy of the commons”—the way rational individual actions can collectively reduce the common good when resources are limited. How this applies to traffic safety may not be obvious. It’s easy to understand that although it pays the selfish herdsman to add one more sheep to common grazing land, the result may be overgrazing, and less for everyone. But what is the limited resource, the commons, in the case of driving? It’s attention. Attending to a sign competes with attending to the road. The more you look for signs, for police, and at your speedometer, the less attentive you will be to traffic conditions. The limits on attention are much more severe than most people imagine. And it takes only a momentary lapse, at the wrong time, to cause a serious accident.

Smeed’s Law, or Why Safety Measures Don’t Improve Safety

What matters most for road safety? The quality of the roads themselves? The engineering of the cars that travel them? The speed limit? The answer may be “none of the above.” In 1949, a British statistician named R. J. Smeed, who would go on to become the first professor of traffic studies at University College London, proposed a now-eponymous law. Smeed had looked at data on traffic fatalities in many different countries, over many years. He found that deaths per year could be predicted fairly accurately by a formula that involved just two factors: the number of people and the number of cars. The physicist Freeman Dyson, who during World War II had worked for Smeed in the Operational Research Section of the Royal Air Force’s Bomber Command, noted the marvelous simplicity of Smeed’s formula, writing in Technology Review in November 2006: “It is remarkable that the number of deaths does not depend strongly on the size of the country, the quality of the roads, the rules and regulations governing traffic, or the safety equipment installed in cars.” As a result of his research, Smeed developed a fatalistic view of traffic safety, Dyson wrote.

Smeed’s Law has worked less well since the mid-1960s; traffic deaths have been somewhat reduced by engineering features such as seat belts and air bags. But technical improvements generally matter less than you might expect, because they affect driver behavior. It’s called “risk compensation”: as cars become safer, drivers tend to take more risks. Psychological factors, in other words, appear to play a huge role in road safety, and they often undercut well-intentioned safety initiatives.

I’ve spent my professional life studying adaptive behavior—how changes in the environment lead to changes in the ways humans and animals act. I’d contend that as traffic signs have proliferated in the U.S., drivers have adapted in profoundly unhealthy ways. We may imagine that driver training is something that happens to 16-year-olds in small cars labeled studentdriver. But of course we spend a lifetime on the roads after we get our licenses, and we’re being trained by our experiences every day. Let’s think about what drivers are actually learning on the roads in America.

Driver Miseducation

Consider the stop sign. It seems innocuous enough; we do need to stop from time to time. But think about how the signs are actually set up and used. For one thing, there’s the placement of the signs—off to the side of the road, often amid trees, parked cars, and other road signs; rarely right in front of the driver, where he or she should be looking.

Then there’s the sheer number of them. They sit at almost every intersection in most American neighborhoods. In some, every intersection seems to have a four-way stop. Stop signs are costly to drivers and bad for the environment: stop/start driving uses more gas, and vehicles pollute most when starting up from rest. More to the point, however, the overabundance of stop signs teaches drivers to be less observant of cross traffic and to exercise less judgment when driving—instead, they look for signs and drive according to what the signs tell them to do.

The four-way stop deserves special recognition as a masterpiece of counterproductive public-safety efforts. Where should the driver look? What must he remember? State driving manuals can be surprisingly coy about exactly what drivers should do at four-way stops. The North Carolina Driver’s Handbook, for example, doesn’t mention four-ways as a separate category at all. Yahoo Answers imparts the following wisdom: “The rules for a four-way stop are like those for a two-way: Stop and look for oncoming traffic, and proceed when it is safe to do so.” So far so good, but then: “You may occasionally arrive at a four-way stop sign at the same time as another driver. In such cases the driver to the right has the right of way. However, not all drivers know this. If someone to your left decides to go first, let them!” Thanks! But remind me: aside from bewildering the driver, what’s the point of stopping traffic in all four directions?

The four-way stop weakens the force of all stop signs by muddling the main question drivers need to answer, namely: Which road has priority? And indeed, American drivers have apparently become confused enough by this question that some communities are now beginning to affix another sign to the poles of stop signs that aren’t four-way, warning cross traffic does not stop.

Speed limits in the U.S. are perhaps a more severe safety hazard than stop signs. In many places, they change too frequently—sometimes every few hundred yards—once again training drivers to look for signs, not at the road. What’s more, many speed limits in the U.S. are set in arbitrary and irrational ways. An eight-lane interstate can have a limit of 50 to 70 mph or more. What makes the difference? A necessarily imperfect guess at probable traffic conditions. The road may sometimes be busy—so the limit is set low. But sometimes the road is not busy, and the safe speed is then much higher than the limit.

A particularly vexing aspect of the U.S. policy is that speed limits seem to be enforced more when speeding is safe. As a colleague once pointed out, “An empty highway on a sunny day? You’re dead meat!” A more systematic effort to train drivers to ignore road conditions can hardly be imagined. By training drivers to drive according to the signs rather than their judgment in great conditions, the American system also subtly encourages them to rely on the signs rather than judgment in poor conditions, when merely following the signs would be dangerous.

Which brings me back to North Glebe Road in Arlington. It turns out that the speed signs do perform an important safety function: in wet weather, many drivers had taken the curve too fast; traffic authorities have substantially reduced accidents on the curve by adding the 15-mph warning sign, and they would be foolish to remove it, absent larger changes in American traffic policy. But this is emblematic of the sort of signage arms race that has become necessary in the U.S. When you’ve trained people to drive according to the signs, you need to keep adding more signs to tell them exactly when and in what fashion they need to adjust their behavior. Otherwise, drivers may see no reason why they should slow down on a curve in the rain.

A Traffic Free-for-All?

So what am I suggesting—abolishing signs and rules? A traffic free-for-all? Actually, I wouldn’t be the first to suggest that. A few European towns and neighborhoods—Drachten in Holland, fashionable Kensington High Street in London, Prince Charles’s village of Poundbury, and a few others—have even gone ahead and tried it. They’ve taken the apparently drastic step of eliminating traffic control more or less completely in a few high-traffic and pedestrian-dense areas. The intention is to create environments in which everyone is more focused, more cautious, and more considerate. Stop signs, stoplights, even sidewalks are mostly gone. The results, by all accounts, have been excellent: pedestrian accidents have been reduced by 40 percent or more in some places, and traffic flows no more slowly than before.

What I propose is more modest: the adoption of something like the British traffic system, which is free of many of the problems that plague American roads. One British alternative to the stop sign is just a dashed line on the pavement, right in front of the driver. It actually means “yield,” not “stop”; it tells the driver which road has the right of way. Another alternative is the roundabout. Roundabouts in the U.S. are typically large. But as drivers get used to them—as they have in the U.K. over the past three or four decades—they can be made smaller and smaller. A “mini-roundabout” in the U.K. is essentially just a large white dot in the middle of the intersection. In this form, it amounts to no more than an instruction to give way to traffic coming from the right (that would be the left over here, of course, since the Brits drive on the left).

As these examples indicate, traffic signs in the U.K. are often on the road itself, where the driver should be looking. And most right-of-way signs are informational: there are almost no mandatory stops in the U.K. (The dominant motive in the U.S. traffic-control community seems to be distrust, and policies are usually designed to control drivers and reduce their discretion. The British system puts more responsibility on the drivers themselves.)

Speed limits in the U.K. are also simpler and better. They are set by road type, so drivers know what limits to expect on highways, rural roads, and urban roads—usually without any signs to tell them. These limits are relatively high, set assuming optimum driving conditions, in contrast to the U.S. limits, which seem to be set with something in between the best and worst conditions in mind. (Precisely where on this spectrum U.S. limits fall seems to vary from road to road, engendering mistrust of the signs in some drivers.) Nonstandard speed limits in the U.K. are rare, so you tend to take them quite seriously when they appear, and they are posted frequently—so you don’t risk missing them if you’re, say, watching the road ahead of you.

I’ve given several talks on traffic in the U.S. and have always found members of the audience to be highly skeptical that the U.K. traffic system could possibly be safer than the one on this side of the Atlantic. As noted, there seem to be more fender benders over here. But not all minor accidents get reported to the police, in either country, and definitions vary. So let’s look at fatalities: everyone agrees on what death is, and fatalities are always reported.

Detailed statistics show that as of 2003, fatalities per mile traveled were 36 percent greater in the U.S. than they were in the U.K. Traffic deaths per million people show an even greater disparity through 2006, the most recent year for which full statistics are available. If the U.S. death rate were the same as the U.K.’s, roughly 6,000 fewer Americans would die each year—that’s half again as many Americans as have died in Iraq in the past five years.

As experimentalists like to remind us, correlation isn’t causation, and differences in traffic-control policies might not be the only reason for this huge difference in traffic deaths. Perhaps people drive slower in Britain? Well, no; in my experience, they usually drive faster. Are cars themselves safer in Britain? Again, probably not; they tend to be smaller, with fewer safety features. It is true that SUVs are more prevalent in the U.S., and that SUVs are often lethal when they hit smaller cars; this likely accounts for some of the difference in fatality rates. But it’s also true, for instance, that when traditional intersections in the U.S. have been replaced by roundabouts, collisions have typically been reduced by about 40 percent, and fatalities by up to 90 percent. And as the U.K. has refined and simplified its traffic-control system over the past 30 years, total traffic fatalities have fallen by about 50 percent. Over the same period, fatalities in the U.S. have declined by just 20 percent; in the past several years, they haven’t declined at all.

I Didn’t See the Gorilla in Front of Me

Conjurers and magicians have long known how to distract people so they miss a move that should be obvious. But it is only recently that social psychologists have come up with dramatic demonstrations of just how tight the limits on our attention can be. One of the most compelling is a 75-second video, by the psychologists Daniel Simons and Christopher Chabris, that shows six male and female students, in black or white T-shirts, passing basketballs to one another. The observer is asked to count the number of passes.

About 45 seconds in, a person in a gorilla suit walks onscreen. She strolls between passers to the center of the screen, faces the camera, beats her chest, and then exits. You can’t possibly miss her—unless, that is, you’ve been instructed to pay attention to the basketballs. When each observer in the experiment was asked, “Did you notice anything unusual in the video?” about half said no. That’s inattentional blindness, the effect of competition for the observer’s attention: by looking for one thing, we miss another that should have been obvious.

The miseducation that U.S. drivers are receiving is not as explicit as the instructions to these students, but it extends over years and is in some ways more forceful: the legal penalties for failing to notice traffic signs are severe. I believe that U.S. traffic policies are inducing a form of inattentional blindness in American drivers. When so many drivers say, after an accident, “I didn’t see him,” they’re not all lying.