Traffic_ Why We Drive The Way We Do Part 5

In a previous study on a campus parking lot-a lot that was crowded but usually had some s.p.a.ces in the back rows-Velkey polled students about how long they thought it typically took them to find a parking s.p.a.ce. "They said four and a half minutes," Velkey told me. "In reality, when we watched them, it takes about thirty seconds. I said, 'Where did that extra four minutes come from?'" Velkey suggests that the psychological principle known as the "availability heuristic" was at work. Students were tending to remember the few times when it was very difficult to find a spot, instead of the everyday experience in which it was quite easy. They were remembering the things that stuck out in their memory.

In the Wal-Mart lot, there was something else interesting about the two groups of parkers. More women seemed to adopt the "cycling" strategy, while more men seemed to opt for the "pick a row, closest s.p.a.ce" tactic. Velkey wondered if a "gender effect" existed in the way women and men perceived distance and travel time (previous studies have arrived at mixed conclusions on this). So he gathered a group of subjects and had them estimate the distance to an object at varying locations, and then asked them to estimate the time it would take them to walk there. Men seemed to underestimate how long it would take to walk, while women seemed to overestimate it-which might explain the differences in parking strategies. Both genders underestimated distances, an effect that grew larger as the distance did.

What had led Velkey, clipboard in hand, to parking lots? Interestingly, it was an offshoot of his prime research interest: the foraging behavior of animals, particularly how animals develop certain strategies in the face of constrained resources such as food or territory. He was studying this at the University of Montana, where wildlife abounds. It turned out there was an interesting example right outside the psych department window: the crowded parking lot. The value of the resource was clear-a faculty member had recently spent a day in jail after keying the car of someone who had stolen his parking spot. (Here we must remember the old dictum about what keeps a university running smoothly: "Beer for the students, parking for the faculty, and football for the alumni.") In this lot, Velkey saw two kinds of behavior emerge: an active and a pa.s.sive search strategy. Some people would drive around the lot looking for a s.p.a.ce, while others would sit at the head of a row and wait for someone to leave. In terms of the avian foraging models Velkey usually studied, the active searchers were like condors, soaring and looking for prey; the pa.s.sive searchers, meanwhile, were like barn owls, perched and lying in wait.

Most people were active searchers, spending about as much time looking as it would take them to drive to the next available lot, while the smaller group would wait for minutes on end for someone to exit. This group, Velkey noted, almost always got a spot in the lot, while others found one elsewhere. (In that study the "postacquisition" costs of walking from the car were not measured, so it is hard to say who came out ahead in terms of total time.) A set of "evolutionarily stable strategies" had taken hold: If everyone tried to be condors, they would all be endlessly circling; if everyone tried to be barn owls, they would all be hovering around the same spot. Depending on circ.u.mstances (e.g., whether cla.s.ses were about to let out), one strategy or another might bring more "local" success than another, but, Velkey notes, eventually everyone gets a spot.

The way humans hunt for parking and the way animals hunt for food are not as different as you might think. Many scientists believe that animals' foraging habits can be explained by a model known as "optimal foraging"-animals seek to gather the most food with the least effort (thus leaving them with more time and energy to, say, reproduce). These strategies evolve in response to the myriad numbers of life-or-death decisions that are made in each successive generation: Does the hunter go after the easy, low-protein prey or the elusive, higher-protein prey? How long does one stay in a particular patch before moving on to a possibly more productive patch? Does one look for food in a group or on one's own?

For some optimal foraging in your own backyard, consider the b.u.mble-bee and the foxglove. Bees, it turns out, begin looking for nectar in the flowers arrayed on the bottom of the spike, slowly working their way up. Why? Because foxgloves add new flowers in an upward progression, so that those at the top contain less nectar. Bees also know to skip flowers they have already visited, and when a new bee lands on a foxglove that has already been visited by another bee, the odds are it will leave immediately. The chances of finding any missed nectar, it seems, are not worth the effort of looking.

Now, instead of bees, think of humans parking. The parkers in the Montana lot who followed the "perching" strategy had evolved a very specific optimal strategy: They knew that near the top of the hour, as cla.s.ses emptied, spots would become available, but it was better to search for the exiting driver driver than the spot. New visitors to the lot, however, or visitors who arrived too late, would circle in vain before ultimately deciding not to expend any more of their energy in this "patch." than the spot. New visitors to the lot, however, or visitors who arrived too late, would circle in vain before ultimately deciding not to expend any more of their energy in this "patch."

In our daily lives as parkers, we face these foraging questions. We must decide whether to act like condors or barn owls. And we're sometimes on the other end: It is not difficult to feel unnervingly like dying prey in the eyes of a stalking buzzard when you come out of a crowded shopping mall during the holidays and suddenly find yourself tailed by a creeping car. Is it faster to tail drivers to their cars and wait for them to load their merchandise or to look for an open s.p.a.ce? Do we pa.s.s up less valuable s.p.a.ces (i.e, "prey") for higher-value s.p.a.ces that might be lurking around the corner? In some cases in the animal world, it is better to hunt for food in groups, but in other cases, going solo is the better option. You may have experienced this dilemma as you cruised the streets of a city (or the rows of a mall) looking for a parking spot, realizing with a sudden dread that the person ahead of you, taillights flas.h.i.+ng hopefully in front of potential s.p.a.ces (which turn out to house fire hydrants or compact cars), is doing exactly the same thing. exactly the same thing. It no longer makes sense to look in the same places, as the car ahead will consume the resource first-better to head elsewhere. It no longer makes sense to look in the same places, as the car ahead will consume the resource first-better to head elsewhere.

But neither animals nor humans always follow optimal strategies. One reason is that not enough information might be available-an issue that the parking industry is trying to address with technology that alerts people, via real-time signage or through cars' navigation systems, to available (paid) parking s.p.a.ces. Another reason might be the cognitive illusions I have already mentioned. Urban planners have pointed out that people seem willing to walk about a half mile from a parking spot to a destination. But they seem more likely to do so when they're walking in the ma.s.sive parking lot to a sports stadium, for example, than on downtown streets. There is an interesting explanation for this: Studies by geographers have shown that people tend to overestimate distances on routes that are "segmented," versus those where the destination is in sight. Thus a football stadium a half mile away in a big parking lot seems closer seems closer than a half-mile walk involving multiple turns in a city. than a half-mile walk involving multiple turns in a city.

The n.o.bel Prizewinning economist Herbert Simon has suggested, in a seminal theory he called "satisficing" (a mix of satisfying satisfying and and suffice suffice), that because it is so hard for humans to always always behave in the optimal way, we tend to make choices that leave us not with the "best" result but a result that is "good enough." To take the bell-curve parking patterns described earlier as an example, drivers may have entered the lot with a general goal of getting the "best" spot, that is, in the row closest to the entrance. Once they were in the row, however, the goal changed to getting the best spot in that row. This is good in that it helps them feel satisfied with the spot they acquire. But if their strategy to get the "best" spot left them worse off overall, it might not be so good. Simon called the human limitations in making decisions "bounded rationality." In Velkey's study, people who focused on finding the "best" parking spot, in terms of distance, failed to account for all the time they were losing while searching-and they didn't get closer anyway. We do not know if they were happy or not with their spot. When Velkey tried to conduct interviews, he was unsuccessful. Ironically, many people said "they didn't have time." behave in the optimal way, we tend to make choices that leave us not with the "best" result but a result that is "good enough." To take the bell-curve parking patterns described earlier as an example, drivers may have entered the lot with a general goal of getting the "best" spot, that is, in the row closest to the entrance. Once they were in the row, however, the goal changed to getting the best spot in that row. This is good in that it helps them feel satisfied with the spot they acquire. But if their strategy to get the "best" spot left them worse off overall, it might not be so good. Simon called the human limitations in making decisions "bounded rationality." In Velkey's study, people who focused on finding the "best" parking spot, in terms of distance, failed to account for all the time they were losing while searching-and they didn't get closer anyway. We do not know if they were happy or not with their spot. When Velkey tried to conduct interviews, he was unsuccessful. Ironically, many people said "they didn't have time."

The ways in which we hunt for parking, whatever their biological basis, are one of those subtle, almost secret patterns of traffic. They matter more than you might think.

Parking occupies a strangely marginal place in the whole traffic equation. Engineers focus their energy on traffic-flow models, not parking models. We do not get morning "parking reports" on the radio. We tend to think of traffic as cars in motion; parking s.p.a.ces seem more like real estate (indeed, they can be priced as high as houses, as the sale of quarter-million-dollar spots in New York and Boston has shown). But the simple, if often overlooked, fact is that without parking there would be no traffic. Every car on the road needs a place where it can begin and end, and mostly just sit there: Cars spend about 95 percent of their time parked.

Parking is the innocuous gateway drug to a full-blown traffic-abuse problem. One survey found that a third of cars entering lower Manhattan were headed to free or subsidized parking spots. If those spots were not free or subsidized, there would be fewer drivers during the morning rush hour. Ironically, near the Department of Transportation itself, the streets are filled with DOT vehicles bearing special parking permits. How much do they add to peak-hour congestion? (This brings to mind a headline from the satirical newspaper the Onion: Onion: URBAN PLANNER SITS IN TRAFFIC OF HIS OWN MAKING. URBAN PLANNER SITS IN TRAFFIC OF HIS OWN MAKING.) When the city of Copenhagen was looking to reduce the number of cars entering the central city in favor of bicycles and other modes of transportation, it had a very crafty strategy, according to Steffen Rasmussen of the city's Traffic and Planning Office: Get rid of parking, but without anyone noticing. From 1994 to 2005, Copenhagen cut parking s.p.a.ces in the city center from 14,000 to 11,500, replacing the s.p.a.ces with things like parks and bicycle lanes. Over that same time, not accidentally, bicycle traffic rose by some 40 percent-a third of people commuting to work now go by bike-and Copenhagen has become one of the few places in the world where one can read, in a report, a sentence that would seem like a comical misprint almost anywhere else: "Cycle traffic is now so extensive that congestion on certain cycle tracks has become a problem, as has cycle parking s.p.a.ce."

What you may not realize, when you find yourself driving on a crowded city street, is that many of your fellow drivers on that crowded street are simply cruising for parking. The problem is not so much the lack of street parking but the plentiful abundance of free or underpriced parking. This finding has sparked the fiery crusade of Donald Shoup, a bearded, bow-tied, and bicycling economist at the University of California, Los Angeles, and the author of a seven-hundred-page, cult-sensation tome t.i.tled The High Cost of Free Parking. The High Cost of Free Parking.

The mantra used by Shoup, and his growing legion of supporters (dubbed "Shoupistas"), is the "85 percent solution." In other words, cities should set prices on parking meters at a level high enough so that an area's spots are only 85 percent occupied at any time. The ideal price, says Shoup, is the "lowest price that will avoid shortages." s.p.a.ces with no meters at all, in a city like New York, are total anathema to Shoup. "People who want to store their car shouldn't store it on the most valuable land on the planet, for free," he told me in his office at UCLA, where a vintage parking meter sits atop his desk. "Something that is free is very misallocated." This is why people who want to see free Shakespeare in the Park performances in New York City have to begin waiting in line as early as the day before (or hire people to do it for them), why cafes that offer free Internet access soon find themselves having to limit the time patrons can spend at a table, and why it can be so hard to find a parking spot.

The reason people cruise is simple: They're hunting for a bargain. In most cities, there is a glaring gap between the cost of a metered parking spot and that of an off-street parking garage. Looking at twenty large U.S. cities, Shoup has found that, on average, garages cost five times five times more per hour than metered street spots. The reason garages can charge so much, of course, is that the streets charge so little. When free parking s.p.a.ces are available, the discrepancy is even higher, particularly for a free spot that can be held for many hours. And so people are faced with a strong incentive to drive around looking for parking, rather than heading into the first available garage. more per hour than metered street spots. The reason garages can charge so much, of course, is that the streets charge so little. When free parking s.p.a.ces are available, the discrepancy is even higher, particularly for a free spot that can be held for many hours. And so people are faced with a strong incentive to drive around looking for parking, rather than heading into the first available garage.

On the individual level, this makes sense. The problem, as is so often the case in traffic, is that the collective result of everyone's smart behavior begins to seem, on a larger scale, stupid. The amount of extra traffic congestion this collective parking search creates is shocking. When Shoup and his researchers tracked cars looking for parking near UCLA (they rode bikes, so other cars would not think they they were looking for parking and throw off the results), they found that on an average day cars in one fifteen-block section drove some 3,600 miles-more than the width of the entire country-searching for a spot. were looking for parking and throw off the results), they found that on an average day cars in one fifteen-block section drove some 3,600 miles-more than the width of the entire country-searching for a spot.

When engineers have tried to figure out how many cars in traffic are looking for parking, the results have ranged from 8 percent to 74 percent. Average cruising times clock in at anywhere from three minutes to thirteen minutes. What's so bad about three minutes? you might ask. As Shoup points out, small amounts can have big consequences. In a city where it takes three minutes to find street parking, and where each s.p.a.ce turns over ten times per day, each of those s.p.a.ces will generate thirty minutes of cruising per day. At 10 miles per hour, that means the average s.p.a.ce generates five miles' worth of driving per day, which works out to a yearly sum that would get you halfway across the United States-not to mention a heap of pollution.

But it is not simply that cars are driving while looking for parking. They're driving in specific ways. There is the inevitable slowing to check out a prospective spot, the stopping to study whether a spot is valid, the actual jockeying into the spot, or what Shoup calls "parking foreplay," in which the person detects that a s.p.a.ce is about to be vacated and stops to wait. This may seem a minor offense, but as I discussed earlier, one car stopped on a two-lane street creates a bottleneck that cuts traffic capacity in half. in half.

This is worsened further by the inevitable delays and gaps caused by drivers battling to merge before they reach the stalled car. One person's small act is felt by many. The famed urbanist William H. Whyte once espied this phenomenon during a traffic study of Manhattan. In his "mind's eye," he observed, one particular street was always "jammed" with double-parked cars (a result of underpriced parking, in Shoup's view). But when he actually counted the number of double-parkers, he was shocked to only find "one or two" at any time. "It seemed odd that so few could do so much," he wrote. "But the number, we found, was not the critical factor. It was the amount of time a lane was out of action because of double parking. Just one vehicle per block was enough."

The more time one spends looking for parking, of course, the greater chance one has to get in a crash, which then creates even more congestion. Interestingly, parking itself, according to some studies, is responsible for almost one-fifth of all urban traffic collisions. While some engineers think curb parking should be done away with entirely for safety and traffic-flow reasons, others counter that the rows of parked cars actually make things safer for pedestrians, both as a physical barrier and a source of "friction," like street trees, that can drop traffic speeds by an estimated 8 miles per hour.

To return to the Wal-Mart study mentioned earlier, the ma.s.sively capacious big-box lots might seem to have little to do with crowded city streets. But there is plenty of cruising in large, free lots. It is simply that the incentive to save money has been entirely replaced by the incentive to save distance (and, theoretically, time, even if that ends up not being the case). In fact, there is always always parking at Wal-Marts, so much so that the company lets people in recreational vehicles treat it like a campground. As Shoup points out, at places like Wal-Mart, the planners who dictate what size the parking lot should design for "peak demand"-that is, Christmas Eve-thus guaranteeing that most of the year, the lot has an abundance of empty s.p.a.ces. The estimated demand comes from the parking-generation models of traffic engineers, which are filled, Shoup notes, with strange irregularities, like the paradoxical fact that banks with drive-up windows are required to have more parking s.p.a.ces than banks without drive-up windows. parking at Wal-Marts, so much so that the company lets people in recreational vehicles treat it like a campground. As Shoup points out, at places like Wal-Mart, the planners who dictate what size the parking lot should design for "peak demand"-that is, Christmas Eve-thus guaranteeing that most of the year, the lot has an abundance of empty s.p.a.ces. The estimated demand comes from the parking-generation models of traffic engineers, which are filled, Shoup notes, with strange irregularities, like the paradoxical fact that banks with drive-up windows are required to have more parking s.p.a.ces than banks without drive-up windows.

Shoup argues that there is a circular logic at work in parking-generation models, one similar to that found in other kinds of traffic models. The demand for parking is treated as a foregone conclusion: Planners measure the number of people parked at a typical free parking lot in a location without much public transportation. The new Wal-Mart is built and, lo and behold, it attracts lots of cars. As Shoup writes, "The parking demand at new land uses with free parking then confirms the prediction that all the required s.p.a.ces are 'needed.'" Planners seem to ignore the fact that they are helping to dictate demand by providing supply. There are lots of cars in lots because parking is free.

As Shoup reminds us, though, Wal-Mart's free parking, like the free curb parking in cities, is not really free; the term is an oxymoron. We pay for "free" parking all sorts of other ways-and not just as a surcharge on the goods we buy. Parking lots are not only the handmaidens of traffic congestion, they're temperature-boosting heat islands, as well as festering urban and suburban floodplains whose rapid storm-water runoff dumps motor oil and carcinogenic toxins like polycyclic aromatic hydrocarbons (from s.h.i.+ny black sealcoat) into the surrounding environment and overwhelmed sewer systems. They represent a depletion of energy and a shockingly inefficient use of land-in a study of one Indiana county, Bryan Pijanowski, a geographer at Purdue University, found that parking s.p.a.ces outnumbered drivers by three to one. three to one. The whole parking equation is like a large-scale version of that person at the mall, circling to get a "better" spot to save time and energy, and not realizing how much time and energy they have wasted looking for a better spot. The whole parking equation is like a large-scale version of that person at the mall, circling to get a "better" spot to save time and energy, and not realizing how much time and energy they have wasted looking for a better spot.

Traffic patterns are the desire lines of our everyday lives. They show us who we are and where we are going. Examined more closely, this movement, like all desires, is not always rational or efficient. Traffic is a great river of opportunity, but often, as with the poor choices made with parking policy, we're just spinning our wheels. In the next chapter, we'll look at some more ways to get unstuck.

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Why More Roads Lead to More Traffic (and What to Do About It) The Selfish Commuter When a road is once built, it is a strange thing how it collects traffic.

-Robert Louis Stevenson

In the summer of 2002, a labor dispute at the ports of Los Angeles and Long Beach halted the flow of goods for ten days. s.h.i.+ps backed up, containers of Nikes and Toyotas lay dormant, and five-axle trucks, the kind that carry the containers from the s.h.i.+ps to their destination, suddenly had nothing to haul. The impact on I-710, the route most trucks take from the ports, was immediate: In the first seven days of the shutdown, there were nine thousand fewer trucks on the highway.

Frank Quon, deputy district director of operations for Caltrans, the state highway authority, noticed something peculiar happening that week. The total total traffic flow dropped by only five thousand vehicles. "Nine thousand trucks disappeared off the system," Quon told me in his office in downtown Los Angeles. So why did the total flow drop by barely over half that? "Cars filled in the volume. Another four thousand cars just jumped in the mix." traffic flow dropped by only five thousand vehicles. "Nine thousand trucks disappeared off the system," Quon told me in his office in downtown Los Angeles. So why did the total flow drop by barely over half that? "Cars filled in the volume. Another four thousand cars just jumped in the mix."

Almost instantly, drivers just seemed to know that the 710, where speeds jumped an average 67 percent during the shutdown, was a good place to be. They may have heard it on the traffic report, or a friend may have told them. Or they took it one day, learned that it was uncongested, and decided to take it the next day as well. What is curious is that the 710 was not necessarily sucking drivers off more crowded routes. "If you look at the parallel routes, like the 110 freeway," Quon said, "the volumes remained essentially the same."

It was as if drivers had suddenly materialized out of nowhere to take advantage of a highway that was, by Southern California standards, almost too good to be true. And it was: By the following week, when the ports reopened, the traffic was even worse than before the shutdown as trucks scrambled to catch up on deliveries-truck traffic, as you might have guessed, jumped much more than the total traffic. Now those new cars were deciding to stay away from the 710.

Engineers like Quon call what happened on the 710 a case of "latent demand." "It's the demand that's there but because the system is so confined that demand doesn't materialize," Quon explained. "But when you create capacity, that latent demand comes back and fills it in." Basically, people who would have never taken the 710 because it was too crowded suddenly got on. We don't really know what they did before. Perhaps they used local streets. Perhaps they took public transportation. Perhaps they simply stayed home.

The point is that people are incredibly sensitive to changes in traffic conditions (sometimes too too sensitive, as we shall soon see) and they seem capable of quickly adapting to even the most drastic changes in a road network. Engineers have a phrase: "It'll be all right by Friday." This rough rule of thumb means that even if on Monday something major happens that throws off the usual traffic patterns-a road is closed, a temporary detour set up-by the next Friday (or so) enough people should have reacted to the change in some way to bring the system back to something resembling normal. "When a change in a traffic pattern occurs, there's a state of flux for a period of time," Quon said. "We usually have everybody plan on expecting a two-week period. Things are going to keep balancing. Some days will be good, some days will be not so good, and then at the end of the two weeks, there will be an equilibrium in the system based on those changes." sensitive, as we shall soon see) and they seem capable of quickly adapting to even the most drastic changes in a road network. Engineers have a phrase: "It'll be all right by Friday." This rough rule of thumb means that even if on Monday something major happens that throws off the usual traffic patterns-a road is closed, a temporary detour set up-by the next Friday (or so) enough people should have reacted to the change in some way to bring the system back to something resembling normal. "When a change in a traffic pattern occurs, there's a state of flux for a period of time," Quon said. "We usually have everybody plan on expecting a two-week period. Things are going to keep balancing. Some days will be good, some days will be not so good, and then at the end of the two weeks, there will be an equilibrium in the system based on those changes."

The latent demand that the newly fast 710 highway in Los Angeles had unlocked is often described by another phrase, "induced travel," which is really just a twist on the same thing: There was a new incentive to drive on the highway. Imagine that instead of trucks disappearing from the 710, two new lanes were added. The result would be the same. Congestion would drop, but the highway would become more attractive to more people, and, when it was all said and done, traffic levels might be even higher than before. This is the "more roads create more traffic" argument you have no doubt heard before. It is actually an argument older than automobile traffic itself. In 1900, William Barclay Parsons, chief of New York City's subway system, wrote, "For New York there is no such thing as a solution to the rapid transit problem. By the time the railway is completed, areas that are now given over to rocks and goats will be covered with houses and there will be created for each new line a special traffic of its own. The instant that this line is finished there will arise a demand for other lines."

Over a century later, people are still arguing. There is a huge and enervating literature about this, which I heartily do not recommend. Do we build more roads because there are more people and more traffic, or does building those roads create a "special traffic all its own"? Actually, both of these things are true. What's in dispute are political and social arguments: Where and how should we live and work, how should we all get around, who should pay for it (and how much), what effect does this have on our environment?

But studies suggest that induced travel is real: When more lane-miles of roads are built, more miles are driven, even more so even more so than might be expected by "natural" increases in demand, like population growth. In other words, the new lanes may immediately bring relief to those who wanted to use the highway before, but they will also encourage those same people to use the highway more-they may make those "rational locators" move farther out, for example-and they will bring new drivers onto the highway, because they suddenly find it a better deal. Walter Kulash, an engineer at Glatting Jackson, argues that road building, compared to other government services, suffers disproportionately from this feedback loop. "You build more roads and you generate more use of the roads. If you add mightily to the sewer capacity, do people go to the bathroom more?" than might be expected by "natural" increases in demand, like population growth. In other words, the new lanes may immediately bring relief to those who wanted to use the highway before, but they will also encourage those same people to use the highway more-they may make those "rational locators" move farther out, for example-and they will bring new drivers onto the highway, because they suddenly find it a better deal. Walter Kulash, an engineer at Glatting Jackson, argues that road building, compared to other government services, suffers disproportionately from this feedback loop. "You build more roads and you generate more use of the roads. If you add mightily to the sewer capacity, do people go to the bathroom more?"

If you do not believe that new roads bring new drivers, consider what happens when roads are taken away. Surely all the traffic must simply divert to other roads, no? In the short term, perhaps, but over time the total level of traffic actually drops. drops. In a study of what they called "disappearing traffic," a team of British researchers looked at a broad list of projects in England and elsewhere where roads had been taken away either for construction or by design. Predictably, traffic flows dropped at the affected area. Most of the time, though, the increase in traffic on alternative routes was nowhere near the traffic "lost" on the affected roads. In a study of what they called "disappearing traffic," a team of British researchers looked at a broad list of projects in England and elsewhere where roads had been taken away either for construction or by design. Predictably, traffic flows dropped at the affected area. Most of the time, though, the increase in traffic on alternative routes was nowhere near the traffic "lost" on the affected roads.

In the 1960s, as Jane Jacobs described in her cla.s.sic book The Death and Life of Great American Cities, The Death and Life of Great American Cities, a small group of New Yorkers, including Jacobs herself, began a campaign to close the street cutting through Was.h.i.+ngton Square Park, in Greenwich Village. Parks were not great places for cars, they suggested. They also suggested a small group of New Yorkers, including Jacobs herself, began a campaign to close the street cutting through Was.h.i.+ngton Square Park, in Greenwich Village. Parks were not great places for cars, they suggested. They also suggested not not widening the nearby streets to accommodate the newly rerouted flow. The traffic people predicted mayhem. What happened was the reverse: Cars, having lost the best route through the park, decided to stop treating the neighborhood as a shortcut. Total car traffic dropped-and both the park and the neighborhood are doing just fine. widening the nearby streets to accommodate the newly rerouted flow. The traffic people predicted mayhem. What happened was the reverse: Cars, having lost the best route through the park, decided to stop treating the neighborhood as a shortcut. Total car traffic dropped-and both the park and the neighborhood are doing just fine.

We have already seen how engineers' models are unable to fully antic.i.p.ate how humans will act on "safer" roads, and it is no different for congestion. It makes sense, mathematically, that if a city takes out a road in its traffic network, traffic on other streets will have to rise to make up for the lost capacity. If you removed one pipe in a plumbing system, the other pipes would have to pick up the slack. But people are a lot more complex than water, and the models fail to capture this complexity. The traffic may rise, as engineers predict, but that in itself may discourage drivers from entering a more difficult traffic stream.

Or it may not. Los Angeles currently operates with a freeway system largely built in the 1950s and 1960s. Its engineers never imagined the levels of traffic the city now sees. As John Fisher, head of the city's DOT, put it, "They say, 'If you build it, they will come.' Because we didn't build it doesn't mean the people stopped coming. Freeways weren't built, but the traffic is still coming anyway. There's more and more traffic. The bottom line is that the L.A. area is going to be a magnet whether we build freeways or not. People are still going to want to come here."

This raises the question of how much more successful a city Los Angeles could be if it had built all the freeways it never did, if one could magically whisk from downtown to Santa Monica in a few minutes. Then again, how desirable would a place like Beverly Hills be if the freeway that had been planned for it, to "cure" L.A. traffic, was now running through it? Wouldn't the increased speed just attract even more more people? Is traffic failing Los Angeles, or is it a symptom of a thriving Los Angeles? Brian Taylor, the planner at UCLA, argues that people often focus single-mindedly on congestion itself as an evil, which, leaving aside for a moment the vast, negative environmental impacts, misses the point: What great city has not been crowded? "If your firm needs access to post-production film editors or satellite-guidance engineers," Taylor notes, "you will reach them more quickly via the crowded freeways of L.A. than via less crowded roads elsewhere." Density, economists have argued, boosts productivity. Traffic engineers like to use the example of an empty restaurant versus a crowded restaurant: Wouldn't you rather eat at the crowded one, even if it means waiting in line? people? Is traffic failing Los Angeles, or is it a symptom of a thriving Los Angeles? Brian Taylor, the planner at UCLA, argues that people often focus single-mindedly on congestion itself as an evil, which, leaving aside for a moment the vast, negative environmental impacts, misses the point: What great city has not been crowded? "If your firm needs access to post-production film editors or satellite-guidance engineers," Taylor notes, "you will reach them more quickly via the crowded freeways of L.A. than via less crowded roads elsewhere." Density, economists have argued, boosts productivity. Traffic engineers like to use the example of an empty restaurant versus a crowded restaurant: Wouldn't you rather eat at the crowded one, even if it means waiting in line?

Users of Match.com, a dating service, are said, in places like Was.h.i.+ngton, D.C., to specify that they would like to meet someone who lives no more than ten miles away, presumably to avoid the ha.s.sles of congestion. Some have seen this as a social problem: Traffic is literally killing killing romance! Cupid is thwarted by congestion! This, too, misses the point: People move to places like Was.h.i.+ngton, D.C., in fact, because there are so many other people nearby. This is why cities play host to speed-dating events. There is so much "romantic congestion" packed into one room that daters must speed through all the potential choices. In Idaho, you will not face traffic trouble in driving well beyond the ten-mile range to meet dates; actually, you will probably have little choice. In any case, as anyone who has been in a long-distance relations.h.i.+p knows, those intervening miles can be a good way of deciding if a potential mate is really worth it. romance! Cupid is thwarted by congestion! This, too, misses the point: People move to places like Was.h.i.+ngton, D.C., in fact, because there are so many other people nearby. This is why cities play host to speed-dating events. There is so much "romantic congestion" packed into one room that daters must speed through all the potential choices. In Idaho, you will not face traffic trouble in driving well beyond the ten-mile range to meet dates; actually, you will probably have little choice. In any case, as anyone who has been in a long-distance relations.h.i.+p knows, those intervening miles can be a good way of deciding if a potential mate is really worth it.

What about all that time wasted in traffic? Surely that is costing us-$108 billion in the United States in 2000, according to one estimate. But a number of economists, most notably Anthony Downs of the Brookings Inst.i.tution, have pointed out the potential flaws in these estimates. The first is that people seem willing to accept much of the delay, instead of paying to eliminate it (which means the "real" loss is closer to $12 billion). Another problem is that some models measure the costs of congestion against a hypothetical ideal of a major city in which all commuters could move at free-flowing speeds during rush hours-a situation that has not been possible since Juvenal's Rome. Still another complication is that models judge the money people lose in traffic by a hypothetical wage rate, but this a.s.sumes that people would get paid for any time saved in traffic-or that they would somehow use the time saved in traveling to do something productive, not simply travel more. more. (As mentioned in the last chapter, many people seem to enjoy the time spent in their car.) Finally, no one really knows how much money we (As mentioned in the last chapter, many people seem to enjoy the time spent in their car.) Finally, no one really knows how much money we make make because of our transportation system, so the losses due to congestion may be marginal. A useful comparison is the Internet. It imposes all kinds of costs on our productivity-YouTube videos, spam, fantasy football-but does anyone not think these are an acceptable cost for all the good we derive from it? because of our transportation system, so the losses due to congestion may be marginal. A useful comparison is the Internet. It imposes all kinds of costs on our productivity-YouTube videos, spam, fantasy football-but does anyone not think these are an acceptable cost for all the good we derive from it?

There is another way, a bit more subtle and complicated, that new roads can cause more traffic: the Braess paradox. This sounds like a good Robert Ludlum novel, but it actually comes from a cla.s.sic 1968 paper by a German mathematician, Dietrich Braess. Put simply, the paradox he discovered says that adding a new road to a transportation network, rather than making things better, may actually slow things down for all its users (even if, unlike in the "latent demand" example, no no new drivers have been induced onto the roads). Braess was actually tapping into the wisdom of a long line of people who had in some way thought about this problem, from the famous early-twentieth-century British economist Arthur Cecil Pigou to operations researchers in the 1950s like J. G. Wardrop. new drivers have been induced onto the roads). Braess was actually tapping into the wisdom of a long line of people who had in some way thought about this problem, from the famous early-twentieth-century British economist Arthur Cecil Pigou to operations researchers in the 1950s like J. G. Wardrop.

You would need an advanced math degree to fully understand Braess and his ilk, but you can grasp the basic problem they were all getting at by thinking in simple traffic terms. First, imagine there are two roads running from one city to another. There is Sure Thing Street, a two-lane local street that always takes an hour. Then there is Take a Chance Highway, where the trip can can be half an hour if it's not crowded, but otherwise also takes an hour. Since most people feel lucky, they get on Take a Chance Highway-and end up spending an hour. From the point of view of the individual driver, this behavior makes sense. After all, if the driver gets off the highway and goes to Sure Thing Street, he or she will not save time. The driver will save time only if others get off the highway-but why should they? be half an hour if it's not crowded, but otherwise also takes an hour. Since most people feel lucky, they get on Take a Chance Highway-and end up spending an hour. From the point of view of the individual driver, this behavior makes sense. After all, if the driver gets off the highway and goes to Sure Thing Street, he or she will not save time. The driver will save time only if others get off the highway-but why should they?

The drivers are locked into what is called a Nash equilibrium, a strategic concept from the annals of Cold War thinking. Popularized by the n.o.bel mathematician John Nash, it describes a state in which no one player of an experimental game can make himself better off by his own action alone. If you cannot improve your situation, why move to a different road? The irony is that when everyone does what is best for him- or herself, they're not doing what is best for everyone. On the other hand, if a traffic cop stood at the junction of the two roads and directed half the drivers to Sure Thing Street and half to Take a Chance Highway, the drivers on Sure Thing Street would get home no sooner, but the highway drivers would get home twice as fast. Overall, the total travel time would drop. drop.

If all this puzzles you, Braess's finding really makes the head spin. To simplify greatly, imagine again the two hypothetical roads I mentioned, but this time imagine that halfway between the two cities, Take a Chance Highway (where the trip takes less than an hour by however many fewer drivers choose it) becomes like Sure Thing Street (always an hour), and vice versa. Since each two-part route is likely to take the same amount of time, drivers split between the two routes, putting us in one-hour equilibrium.

But now imagine that a bridge is built connecting the two roads, right at the halfway point where Take a Chance becomes Sure Thing, and vice versa. Now drivers who began on Take a Chance Highway and found that it was not so good take the bridge to the other other Take a Chance Highway segment. Meanwhile, drivers who began on Sure Thing Street are not about to cross the bridge and move to the other Sure Thing Street when, instead, they could stick around as their road becomes Take a Chance Highway (who knows, they might get lucky). Take a Chance Highway segment. Meanwhile, drivers who began on Sure Thing Street are not about to cross the bridge and move to the other Sure Thing Street when, instead, they could stick around as their road becomes Take a Chance Highway (who knows, they might get lucky).

The problem is that if everyone tries to do what they think is the best thing for themselves, the actual travel time for all drivers goes up! The new link, designed to reduce congestion, has made things worse. The reason lies in what computer scientist Tim Roughgarden has called "selfish routing." The way each person is moving through the network seems best to them ("user optimal"), but everyone's total behavior may be the least efficient for the traffic network ("system optimal").

This really brings us to the heart of traffic congestion. We are "selfish commuters" driving in a noncooperative network. When people drive to work in the morning, they do not pause to consider which route they could take to work, or at which time to take that route, so that their decision would be best for everyone else. They get on the same roads and wish that not so many others had also chosen to do the same thing.

As drivers, we are constantly creating what economists call, in the th.o.r.n.y language of economics, "uninternalized externalities." This means that you are not feeling the pain you are causing others. Two legal scholars at the University for California at Berkeley have estimated, for example, that every time a new driver hits the road in California, the total insurance cost for everyone else goes up by more than $2,000. We do not pay for the various unsavory emissions our cars create-to take just one case, the unpaid cost of Los Angeles' legendary haze is about 2.3 cents per mile. Nor do we pay for the noise we create, estimated by researchers at the University of California, Davis, to be between $5 billion and $10 billion per year. How can you estimate the cost of something like noise? Real estate provides a clue. Studies have shown that house prices decline measurably as traffic rates and speeds increase on the adjoining street, while, on the other hand, when traffic-calming projects are installed on streets, house prices often rise. One might argue that the lower price of a house on a high-traffic street already takes into account these costs, but what happens when a buyer purchases a house at a certain price and then traffic increases on that street, lowering its value? Living near a major road also exposes people to more hydrocarbons and particulates of car exhaust, and any number of studies have reported links between proximity to traffic and conditions like asthma and coronary problems.

There are other kinds of costs, more difficult to measure, that you as a driver put on the people you drive by. When the urban planner Donald Appleyard surveyed San Francisco in the 1970s, he found that on streets with more road traffic, people had fewer friends and spent less time outside. In the same way that traffic has been blamed for habitat fragmentation of the wild, cutting off species from foraging areas or reducing the tendency of birds to breed, high traffic helps starve social interaction on human streets (maybe this this is how congestion hurts romance). Somewhat paradoxically, Appleyard found that people who lived on the streets with less traffic (who made more money and were more likely to own their homes) actually is how congestion hurts romance). Somewhat paradoxically, Appleyard found that people who lived on the streets with less traffic (who made more money and were more likely to own their homes) actually created more traffic themselves, created more traffic themselves, while the people who lived on the high-traffic streets were less able to afford cars. The rich, in effect, were taxing the poor. while the people who lived on the high-traffic streets were less able to afford cars. The rich, in effect, were taxing the poor.

The most basic externality, however, is congestion itself. Your presence in the traffic stream helps add time to others' commutes, just as others' presences add time to yours. But no one driver is gaining more than those others are collectively losing. In economics, a "public good" is something that a person can consume without reducing someone else's ability to consume that same thing or exclude them from doing so-sunlight, for example. An empty road late at night might be thought of as a public good, but a road with any kind of congestion on it quickly becomes "subtractable"-the more people who use it, the worse it performs.

This is the famous "tragedy of the commons," as described by Garret Hardin, in which a pasture open to all is quickly filled up by herders who want to graze as many cattle as possible. Every time a herder adds a cow, he gains. The pasture eventually begins to suffer from overgrazing, but a herder still still adds animals because he alone benefits from his gain, even if the returns are diminis.h.i.+ng (and they ultimately vanish), while everyone shares the costs of that new animal. (Overfis.h.i.+ng is another such oft-invoked "tragedy.") adds animals because he alone benefits from his gain, even if the returns are diminis.h.i.+ng (and they ultimately vanish), while everyone shares the costs of that new animal. (Overfis.h.i.+ng is another such oft-invoked "tragedy.") The "tragedy of the highway" is seen as every car joins the peak-hour freeway. As each car gets on, things get worse for everyone, but as there is still a gain for each driver (getting to work, getting home) that exceeds the gain from not driving, and as the loss is shared by all, people keep joining the freeway.

A Few Mickey Mouse Solutions to the Traffic Problem 98% OF U.S. COMMUTERS FAVOR OF U.S. COMMUTERS FAVOR.

PUBLIC TRANSPORTATION FOR OTHERS.

-headline in the Onion Onion

So how can traffic congestion, this age-old dilemma, be solved? "Build more roads!" is a typical answer. "But more roads bring more traffic!" is the typical response. "Then build even more roads!" "But that will bring even more traffic!" Looking beyond that hall of mirrors, it's worth pointing out a few things. The most obvious problem with building more roads to alleviate congestion is that we, in the United States at least, cannot afford them. Talk to just about any traffic engineer and they will repeat what the numbers already tell us: We do not have enough money to maintain the current current roads, much less build new ones. What about all those fuel taxes? Drivers in the United States pay one-half the fuel taxes of drivers in Canada, one-fourth that of the j.a.panese, and roads, much less build new ones. What about all those fuel taxes? Drivers in the United States pay one-half the fuel taxes of drivers in Canada, one-fourth that of the j.a.panese, and one-tenth one-tenth of the English. Adjusted for inflation, the fuel tax brings in less revenue than it did in the 1960s. of the English. Adjusted for inflation, the fuel tax brings in less revenue than it did in the 1960s.

But even if we could afford to build more roads, that might not be the best way to spend the money. For one, as the transportation scholar Martin Wachs has pointed out, "Well over 90 percent of our roads are uncongested for well over 90 percent of the time." Many congested roads are congested for only a few hours a day, which brings up the Wal-Mart parking lot problem of the previous section. Do you build a parking lot that will be below capacity for 364 days of the year so that it can accommodate every shopper on Christmas Eve? On the one hand, it might be a socially negative thing that some people have to get on the roads at five a.m. in Los Angeles to make it to work on time, or that both directions of the highway are crowded at many hours of the day. On the other hand, this is a good thing. It means the road network is being used efficiently. Empty roads may be fun to drive on, but they're also wasteful.

Adding more lanes to a road is not always the traffic-busting silver bullet you might think it is. Imagine that you're at the extremely crowded intersection of two three-lane roads. Why can't they make it bigger? you ask. Look at all those people who want to turn left-why can't they add another left-turn lane? The problem, as two Canadian researchers have pointed out, is that adding more lanes is a process of diminis.h.i.+ng returns.

The bigger intersections grow, the less efficient they become. Adding a second left-turn lane, for instance, means that, for safety reasons, "permissive" (or on the green) left turns can no longer be allowed. Only "protected" left turns (on the green arrow) will be allowed. As fewer cars can now turn left on the green signal (through gaps in oncoming traffic), the arrow phase will have to be longer. This means most other movements have to be halted. More lanes also mean more "friction," as engineers call it; a car wanting to turn left, for example, will find it harder going-and have a greater impact on the total traffic flow-when it has to cross three lanes instead of one. Given that bigger intersections take longer to cross, the clearance phase-that dead zone engineers introduce to make sure everyone has gotten through, including pedestrians-needs to become longer as well, further increasing delay. The result is that where an intersection with a single-lane approach would handle an average of 625 vehicles per hour, the next lane allows only 483 vehicles per hour, the third 463, and the fourth just 385. The more you spend on new lanes, the smaller the return-and the faster it becomes recongested.

Another problem is that most traffic jams are what engineers call "nonrecurring congestion." This means a highway that normally functions fine is congested, perhaps because of construction or weather but, most often, because of crashes. Rather than build more lanes, the best congestion solution here is for people to get in fewer crashes-which, as described in Chapter 3, would happen if drivers simply paid more attention to their driving.

The actual crash, which may or may not close a lane, is only part of the problem, of course. The highway's capacity drops an estimated 12.7 percent because of the line that forms-often on both both sides of the highway-to take a look. This is where human psychology fails us. Not only do we have a morbid curiosity to rubberneck, but we feel we should not miss out on what others have had a chance to see. The economist Thomas Sch.e.l.ling points out that when each driver slows to look at an accident scene for ten seconds, it does not seem egregious because they have already waited ten minutes. But that ten minutes arose from everyone else's ten seconds. Because no individual suffers from the losses he inflicts on others, everyone is slowed. "It is a bad bargain," concludes Sch.e.l.ling. The ubiquity of cell phone cameras is making things worse, as "digi-neckers" slow things even more to take photos of incidents. To top it off, drivers looking at crashes quite often get into crashes themselves. A study by researchers at Virginia Commonwealth University found that the second-leading cause of distraction-related crashes (behind fatigue) was "looking at crashes, other roadside incidents, traffic, or other vehicles." sides of the highway-to take a look. This is where human psychology fails us. Not only do we have a morbid curiosity to rubberneck, but we feel we should not miss out on what others have had a chance to see. The economist Thomas Sch.e.l.ling points out that when each driver slows to look at an accident scene for ten seconds, it does not seem egregious because they have already waited ten minutes. But that ten minutes arose from everyone else's ten seconds. Because no individual suffers from the losses he inflicts on others, everyone is slowed. "It is a bad bargain," concludes Sch.e.l.ling. The ubiquity of cell phone cameras is making things worse, as "digi-neckers" slow things even more to take photos of incidents. To top it off, drivers looking at crashes quite often get into crashes themselves. A study by researchers at Virginia Commonwealth University found that the second-leading cause of distraction-related crashes (behind fatigue) was "looking at crashes, other roadside incidents, traffic, or other vehicles."

What this means is that, at times, we have a perfect self-generating traffic jam: People slowing to look at crashes get into crashes, which causes other people to get into crashes, and so on. If traffic were a cooperative network and we could agree not to slow and look, Sch.e.l.ling notes, everyone could save time. Since that will never happen, traffic engineers have instead countered with antirubbernecking screens, which can be unfurled at crash scenes to block prying eyes. In theory these should help matters, but they have severe limitations. Just getting a screen to a crash site, past the traffic that has already developed, is hard enough. Then picture emergency responders, who probably have more pressing matters to attend to, trying to erect-in strong winds or snow-a giant wall of fabric, as if imitating the artist Christo. Plus, ironically, there is the interest in the screen itself. Janet Kennedy, a researcher at England's Transport Research Laboratory, told me the screens had been tried on construction projects on the M25 motorway. "To start with it didn't have much effect because people just looked at the screen anyway," she said. "But already we're finding people have stopped looking at the screen. They're used to it." That's fine for construction sites, which the same people drive past each day. Unfortunately, this suggests that for crashes, the events that generate the most rubbernecking, the screens are of little help-the crash would be cleared long before drivers became accustomed to seeing the same screen.

But what about the congestion that's "recurring," that happens on the same roads every day? If money was available, we could build more lanes. Only this still does not get us past the pasture problem: Create a bigger pasture, and people will bring even more cows. Traffic congestion is a kind of two-way trap. Because driving is a bargain (drivers are not picking up the full tab for the consequences of their driving), it attracts many people to roads that are not fully funded; this not only makes them crowded, it makes it hard to find revenue to build new ones.

When Costco discounts televisions during its Christmas shopping promotions, pricing them so low that stores do not make a profit, what happens? There are huge lines at the door at five a.m. When cities provide roads that are priced so low that they lose money on them, what happens? There are huge lines on the highway at five a.m. Pricing changes behavior. This is hardly a revelation, but it's always striking to see it in action. At a Pizza Hut in Beijing, I watched with some wonder as patrons at the salad bar carefully arranged towering piles of salad on their plates, then carefully walked away with mounds of teetering greens. Why did they do this? There was a flat fee for one visit, so patrons made sure they got their money's worth. They traveled as efficiently as they could. What if the fee was good for unlimited visits to the salad bar? People would have made multiple trips, carrying smaller portions of salad. The traffic flow back and forth to the bar would have gone up.

In traffic, the basic model has been a state-subsidized, all-you-can-eat salad bar. Take as many trips on the roads as you like, whenever you want, for whatever reason. It may be a good deal for society-a loss leader, like Costco's cheap televisions-but it's such a good deal that everyone does it. Recently, however, as we have been running out of money and s.p.a.ce for new roads, the thinking has turned from "How can we get more people on the roads?" to "How can we get fewer?" The answer, of course, is congestion pricing. As an idea, it's hardly new. The idea of taxing people for the "externalities," like congestion, that they create goes all the way back to economists like Arthur Pigou, who talked about the problems road users create for other road users in his 1920 book, The Economics of Welfare. The Economics of Welfare.

Later, the n.o.bel Prizewinning economist William Vickrey led a long, lonely crusade to get people to accept the idea that urban roads are a scarce resource and should be priced accordingly. After all, as Vickrey pointed out in 1963, hotels charge more for in-season rooms, railways and airlines charge more for peak travel periods, and telephone companies charge more during the times when more people are likely to call-why should roads not cost more when more people want to use them? (Vickrey was a bit ahead of his time: Told in the early 1960s that there was no way to track where people drove, or how much they drove, Vickrey, the story goes, built a cheap radio transmitter and installed it in his car, displaying the results to friends.) Congestion charging, in cities like London and Stockholm, has been shown to work because it forces people to make a decision about-and gives them a precise benchmark against which to measure-whether a given trip is "worth it." We may have been paying before, in time time-which hardly helps fund the roads-but the human mind handles time differently than money. We seem less sensitive to the value of time, even if, unlike money, time can never be regained. It is easier for people to rationalize its loss. The problem with the crowded highway is that everyone suffers the same loss of time, even if some people's use of the highway might be worth more to them-to take an extreme example, think of a woman about to give birth on the way to the hospital, stuck in a traffic jam alongside someone who simply "needed to get out of the house." They may each feel that their trip is valid, but is that really how a scarce resource should be distributed?

When people are forced, by means of how much it will cost them, to think about when, where, and how they are going places, interesting things begin to happen. You might a.s.sume that a rush-hour highway is filled with people driving to work who have no other way to get there-and no other time they can travel-but studies suggest that this is not the case. When researchers have exhaustively tracked the license plates of every car traveling on rush-hour highways and matched the results to other days, they have typically found that only about 50 percent are the same people each day. Sometimes people's patterns emerge when you look deeper into what would seem to be random behavior. In what the English traffic researcher Richard Clegg calls the "See you next Wednesday effect," research has found that when people use a rush hour on Wednesday of one week, they're more likely to be on that same highway on the next Wednesday than on another day.

Not everyone is so rigid in their habits. In 2003, a group of drivers in Seattle were outfitted with electronic devices that would tell researchers where and when they had driven. Baseline data was collected on these people's typical habits. Then the drivers were informed that they would be given a hypothetical cash account. They would automatically be charged more for driving in the most crowded places at the most crowded times. Matthew Kitchen, director of the Puget Sound Regional Council, the group that sponsored the program (called Traffic Choices), said he was struck by how differently people acted day to day even before before they were charged tolls. they were charged tolls.

Once the tolls kicked in, things really began to change: People left sooner, took different routes, took buses, "collapsed" trips into shorter bundles. "The reality which is emerging is that I think people are very intelligent agents, working on their own behalf," he said. "They understand the unique trade-off they face between time and money. The range of response is extremely broad. For instance, my willingness to pay to save ten minutes today might be very different than tomorrow."

How much did the charging affect driving? The total "tours," as they are called in transportation-planning lingo, dropped by 13 percent. That may not seem like much, but in the world of bottlenecks, small changes can have big effects (a 5 percent drop in traffic, it is said, can increase speeds by 50 percent, even if that only means going from 5 to 10 miles per hour). With traffic jams, Kitchen noted, "Once you start falling off the cliff, you fall pretty fast and pretty hard. That's why between 5 and 10 percent less traffic restores what are really credible speeds on the network. You don't have to hit people over the head with something that is punitive. You can achieve reasonable results with incentives that result in fairly modest behavioral response."

By getting just some people to change their behavior, congestion pricing can help reverse a long-standing vicious cycle of traffic, one that removes the incentives to take public transportation. Th