Per chi passa buona parte della sua giornata su strade e autostrade il libro da leggere è “Traffic” di Tom Vanderbilt. Un “must”. Contiene tutti i segreti che si nascondono nel traffico urbano ed extraurbano.
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Perché, per esempio, la fila che ci sta accanto avanza più velocemente?
Semplice, è solo un’impressione: le macchine che ci superano procedono in modo sgranato mentre le macchine che superiamo sono allineate in modo compatto: passiamo molto più tempo ad essere superati che a superare.
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Se la strada passa da due a una corsia quando è meglio “rientrare”?
Risposta: il più tardi possibile.
Motivo: così si contribuisce ad occupare più razionalmente la strada e si evitano gli sprechi di asfalto.
Un esempio iperbolico chiarisce. La Gallarate-Varese termina con un maledetto “collo di bottiglia” che di fatto trasforma l’autostrada a due corsie in una bretella a corsia unica. In altri termini, la corsia di sinistra dell’autostrada viene gradualmente eliminata. Supponiamo ora che il restringimento sia segnalato già a Gallarate e che la gente voglia convergere “il prima possibile” oppure “quando ne ha l’opportunità”, ben presto tutti viaggerebbero sulla corsia di destra e l’autostrada si trasformerebbe di fatto in una strada a corsia unica. Che spreco assurdo!
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Perché in macchina diciamo cose irripetibili all’indirizzo degli altri autisti imbranati?
Qui la risposta è facile, specie dopo l’avvento dei social: l’isolamento e il senso di anonimato ci disinibisce e ci rende più aggressivi.
Ma c’è si più.
Il fatto è che noi ci muoviamo su mezzi del XX secolo ma nella testa siamo ancora tanti Fred Flinstones…
… Jay Phelan, an evolutionary biologist who works a few buildings over from Jack Katz at UCLA, often thinks about traffic as he pilots his motorcycle through Los Angeles. “We evolved in a world in which there were about a hundred people in the group you were in,” he says. “Every person you saw you had an ongoing relationship with.” Was that person good to you? Did they return the spear they borrowed last week? This way of getting along is called “reciprocal altruism.” You scratch my back, I’ll scratch yours; we each do it because we think it will benefit us “down the road.” What happens in traffic, Phelan explains, is that even though we may be driving around Los Angeles with hundreds of thousands of anonymous others, in our ancient brains we are Fred Flintstones (albeit not driving with our feet), still inhabiting our little prehistoric village. “So when someone does something nice for you on the road, you’re processing it like, ‘Wow, I’ve got an ally now.’ The brain encodes it as the beginning of a long-term reciprocal relationship.”…
La nostra aggressività è in realtà un comportamento altruistico: cooperiamo d’istinto con la nostra banda.
Perché infatti dovremmo “punire” uno che non vedremo presumibilmente mai più? C’è solo un motivo: perché in futuro si comporti bene con gli altri…
… This sense of fairness might cause us to do things in traffic like aggressively tailgate someone who has done the same to us. We do this despite the costs to our own safety (we might crash, they might be homicidal) and the fact that we will never see the person we are punishing again… The Swiss economist Ernst Fehr and his colleagues have proposed a theory of “strong reciprocity,”36 which they define as “a willingness to sacrifice resources for rewarding fair and punishing unfair behavior even if this is costly and provides neither present nor future material rewards for the reciprocator.”… So perhaps, as the economist Herbert Gintis suggests, certain forms of supposed “road rage” are good things…
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Come migliorare i rapporti con gli altri automobilisti?
Cercando i loro occhi…
… When you need to do something like change lanes, however, eye contact is a key traffic signal…
Gli occhi dell’altro sono importanti. Ne volete una prova?…
… Because eye contact is so absent in traffic, it can feel uncomfortable when it does happen. Have you ever been stopped at a light and “felt” someone in a neighboring car looking at you? It probably made you uneasy. The first reason for this is that it may violate the sense of privacy we feel in traffic…
La forza dello sguardo…
… Many studies have confirmed this: Eye contact greatly increases the chances of gaining cooperation in various experimental games (it worked for Seinfeld’s George, by the way). Curiously, the eyes do not even need to be real. One study showed that the presence of cartoon eyes on a computer screen made people give more money to another unseen player than when the eyes were not present.40 In another study, researchers put photographs of eyes above an “honor system” coffee machine in a university break room…
Gli occhi dovrebbero essere cercati ogni volta che è possibile, specie dai ciclisti.
Sei un ciclista e devi cambiare corsia? Girati e guarda indietro, magari non incrocerai gli occhi dell’auto che ti segue e che ti sta superando ma darai l’impressione di gettare uno sguardo e la cosa la farà senz’altro rallentare.
A proposito di ciclisti, come circolare in modo sicuro?
Mantenere la destra senza schiacciarsi ma prendendosi un buon margine, il che aumenta l’attenzione di chi vi sorpassa. Simulare poi qualche leggera sbandatina aiuta nello scopo di sviluppare una maggiore prudenza nell’automobilista in arrivo.
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Guidare è facile?
No, è incasinatissimo. Forse è la cosa più difficile che facciamo nella vita, anche più difficile del nostro lavoro…
… For those of us who aren’t brain surgeons, driving is probably the most complex everyday thing we do…
Tanto è vero che i robot non riescono ancora a farlo.
Guidare ci sottopone ad una serie di dilemmi. Ecco il dilemma del semaforo…
… Engineers call the moment when we’re too close to the amber light to stop and yet too far to make it through without catching some of the red phase the “dilemma zone.” And a dilemma it is… In traffic, these sorts of dilemma zones occur all the time…
Guidare è difficile ma ci viene bene. Per quello che a molti piace guidare, perché una cosa che ci rende felici è fare cose difficili che ci vengono naturali (teoria del “flow”).
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Perché non riusciamo a capire come guidiamo?
Perché mancano i feedback. Sono rarissimi.
Qualcuno propone un meccanismo reputazionale come su ebay…
… What if there was an eBay-like system of “reputation management” for traffic? This idea was raised in a provocative paper by Lior J. Strahilevitz…
C’è anche chi ha preso sul serio la cosa…
… Less ambitious and official versions of this have been tried.16 The Web site Platewire.com, which was begun, in the words of its founder, “to make people more accountable for their actions on the roadways in one forum or another,” gives drivers a place to lodge complaints about bad drivers, along with the offenders’ license plate numbers; posts chastise “Too Busy Brushing Her Hair” in California and “Audi A-hole” in New Jersey. Much less frequently, users give kudos to good drivers…
Poi c’è la psicologia: se nessuno che rispettiamo ci dice ripetutamente che facciamo schifo noi crediamo di essere bravi…
… Monty Python: “We Are All Above Average!” Psychologists have called this phenomenon “optimistic bias” (or the “above-average effect”), and it is still something of a mystery why we do it. It might be that we want to make ourselves out to be better than others in a kind of downward comparison, the way the people in line in the first chapter assessed their own well-being by turning around to look at those lesser beings at the back of the queue. Or it might be the psychic crutch we need to more confidently face driving, the most dangerous thing19 most of us will ever do…
In sé non è negativo: avere fiducia in se stessi forse ci fa guidare meglio. Certo che un giudizio più credibile rassicurerebbe.
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La strada non è certo il nostro ambiente naturale, le illusioni cognitive si susseguono e ci mettono in pericolo.
Stare sempre attenti è quasi impossibile, il blind spot è la norma…
… You realize, with a mixture of wonder and horror, that you cannot remember what you have been doing for the past few moments—nor do you know how long you have been “out.”…
Cosa ho fatto nei 10 secondi precedenti? Boh, di certo andavo a 140 all’ora in autostrada. Speriamo in bene.
La chiamano “ipnosi dell’autosrada”.
Il problema è che noi non sappiamo bene quanta attenzione dedicare alla guida…
… What is also unclear is how much attention we were actually paying to the road while under the spell of highway hypnosis…
Il problema è che la guida non merita TUTTA la nostra attenzione (siamo bravissimi) e a volte un’attività complementare non è disponibile.
Spiego meglio. L’abitudine è il nostro pilota automatico…
… Driving, for most of us, is what psychologists call an “overlearned” activity. It is something we’re so well practiced at that we’re able to do it without much conscious thought… the better we become at it, the less we think of each individual step… The more overlearned an activity becomes, the less cognitive workload it imposes…
Ci resta una riserva (finita) di attenzione. Come impiegarla per raggiungere il giusto bilanciamento? Qualcuno non la impiega e si annoia, il che non è bene…
… Too little workload has its own problems. We get bored. We get tired. We lapse into highway hypnosis. We may make errors…
Qualcuno trova altri impegni…
… Most driving rarely requires our full workload. So we listen to the radio, look out the window, or, increasingly, talk on the cell phone or read text messages—in the case of one fatal crash in California, the driver may have been operating a laptop computer as he drove…
Sia chiaro: ogni attività assorbe parte delle nostre risorse di attenzione, non ci sono “pasti gratis”. Se guidiamo e parliamo saremo dei cattivi conversatori…
… This raises another point: Researchers look at how driving is affected when people do other things, but research also shows that secondary tasks suffer as well. We become worse drivers and worse talkers… It’s like speed-reading. You think you can read really fast but your comprehension disappears…
In questo senso il multitasking è un mito…
… we buy into the myth of multitasking with little actual knowledge of how much we can really add in or, as with the television news, how much we are missing…
Se il (difficile) calcolo delle attività complementari è fatto male… sono guai…
… The sources of distraction inside a car have been painstakingly logged by researchers. We know that the average driver adjusts their radio 7.4 times per hour of driving, that their attention is diverted 8.1 times per hour by infants, and that they search for something—sunglasses, breath mints, change for the toll—10.8 times per hour.8 Research has further revealed just how many times we glance off the road to do these things and how long each glance takes: In general, the average driver looks away from the road for .06 seconds9 every 3.4 seconds…
E’ la distrazione che causa incidenti, non l’incapacità. Un guidatore incapace al massimo fa incazzare chi lo segue.
Gli incidenti si fanno quasi sempre vicino a casa.
Dice: ovvio. Sono le strade che battiamo di più. No, resta vero anche se teniamo conto di questo fatto. E’ che nelle zone familiari l’attenzione cala.
Difficilmente faremo mai un incidente guidando su una strada di montagna che non conosciamo bene.
Da qui il noto paradosso del volante: più una strada è pericolosa, più è sicura.
O meglio: le strade più pericolose sono quelle che “appaiono” più sicure.
Mettere qua e là degli ostacoli, anche artificiosi, rende più prudenti. Gli automobilisti si adattano alla strada.
Insomma, calcolare e redistribuire in modo oculato l’eccesso di attenzione è il problema maggiore di chi guida…
… The drivers were redistributing workload. With more of their attention devoted to a cell phone conversation, they may have had to work just a bit harder to stay in their lane… Something similar happens with very new drivers on highways: So much of their mental concentration is devoted to simply staying in the lane, they have trouble paying attention to their speed…
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In movimento noi non vediamo la realtà per come è. Esperimento: calcola la distanza tra le linee tratteggiate di mezzaria…
… Try to picture, for a moment, the white stripes that divide the lanes on a major highway. How long would you guess they are? How much space would you say lies between each stripe? When first asked this question… I use this as a simple example of how what we see is not always what we get as we move in the unnaturally high speeds of traffic…
Il falcone pellegrino, lui sì che sa guardare mentre viaggia (a 130 km orari)…
… As the naturalist Robert Winkler points out, creatures like hawks, whose eyes possess a much faster “flicker fusion rate” than humans’, can track small prey from high above as they dive at well over 100 miles per hour.50 The short answer is that we cheat…
Ecco un buon adesivo da mettere sul retro della vostra auto…
… IF YOU CAN READ THIS, YOU’RE TOO CLOSE…
E’ il movimento delle cose ci frega, le illusioni ottiche si moltiplicano…
… the spokes on a car’s wheels sometimes seem to be moving “backward.” This so-called wagon-wheel… we perceive the world not as a continuous flow but in a series of discrete and sequential “frames.”…
Quando usciamo dall’autostrada piombiamo come falchi sulla città pensando di essere quasi fermi (speed adaptation)…
… in some places, engineers have tried to exploit this by employing “illusory pavement markings”54 to make drivers think they are going faster than they are… These experiments have been focused on exit ramps because they are a statistically dangerous part of the highway… The longer we drive at high speeds, the harder it is for us to slow down…
Delle colonnine frequenti ai lati possono essere utile a realizzare quanto succede realmente.
D’altronde, ingombrare i lati ci fa sempre rallentare (a parità di spazi nella carreggiata). Le barriere acustiche, per esempio, producono un rallentamento.
In molti centri urbani si invitano i bar a mettere la terrazza anche a fianco delle strade per rallentare il traffico. Le macchine procederanno a passo d’uomo.
A Varese quando si vuole pedonalizzare una strada prima la si riempie di tavolini e sedie. Il traffico è ancora aperto, la carreggiata esattamente come prima ma le auto sono molto più timide, vanno a passo d’uomo e si sentono fuori luogo.
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Il traffico delle formiche è il traffico perfetto. Come lo gestiscono loro non lo gestisce nessuno…
… the New World army ant, or Eciton burchellii, and these insects may just be the world’s best commuters. Army ant colonies are like mobile cities, boasting populations that can number over a million. Each dawn, the ants set out to earn their trade. The morning rush hour begins a bit groggily, but it quickly takes shape…
Perché non lo imitiamo?
Perché le formiche hanno un obbiettivo comune, noi uno per ogni automobilista. Per loro è più facile collaborare…
… The secret to the ridiculous efficiency of army ant traffic is that, unlike traveling locusts—and humans—the ants are truly cooperative…That Oscar afternoon was a small but perfect illustration of how complicated human traffic is when compared to ant traffic…
Poi loro viaggiano da millenni, noi da poco…
… Ants have evolved over countless centuries to move with a seamless synchronicity that will benefit the entire colony…
Prendi un lamento comune: “ma perché non sincronizzano i semafori in modo che siano tutti verdi?”…
… Take traffic signals. It’s common to hear drivers in Los Angeles, as elsewhere, lament, “Why can’t they time the signals so they’re all green?” The obvious problem with so-called synchronized signals is that there is a driver moving in a different direction asking the same thing… Engineers can use sophisticated models to squeeze as much “signal progression” as possible out of a network, to give the driver the “green wave.”…
Ovvia risposta: perché c’è gente che va in direzioni diverse. Si fa quel che si puo’, non siamo formiche che collaborano.
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Il segreto delle formiche è la velocità costante.
Il senso comune non riesce a rendere quanto giovi questo fatto, ovvero quanto sia problematico un blocco del traffico: un minuto di blocco, cinque di ritardo…
… Engineers at Caltrans say that as a rule of thumb, for every one minute a highway lane is blocked, an additional four to five minutes of delay are generated… The economist Thomas Schelling 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…
Perché? Perché tra le auto c’è una specie di “attrito” anche quando non si toccano, basta la contiguità.
Sì, c’è anche se non si toccano. La vicinanza alle altre auto innesca problemi di comunicazione e crea incertezza.
Prendi i tempi di reazione: se ci fermiamo e ripartiamo più veloci impieghiamo più tempo rispetto a chi viaggia in un flusso a velocità costante.
Una colonna di macchine ferme che riparte accumula tutti i ritardi insiti nei vari tempi di reazione di chi è chiamato di volta in volta a muoversi. i singoli ritardi sono minimi ma il cumulo è notevole
Per questo si dice che “il traffico lento va più veloce”. per questo fioccano i sensi unici e i ring nelle nostre città.
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Perché certe autostrade vengono chiuse (ramp meters) anche quando scorrono?
Perché scorrono grazie all’ingresso selezionato.
Il motivo è quello di prima: fare in modo che la velocità costante prevalga sulla “fisarmonica”.
L’attrito tra macchine (o car following) è forse l’elemento chiave della circolazione…
… The first efforts merely tried to model the process known as “car following.” This is based on the simple fact that the way you drive is affected by whether or not someone is in front of you, and how far away or close they are… you’re influenced by the driver ahead… Do you feel uncomfortable driving next to someone else, and therefore speed up or slow down? Are you sometimes willing, for no apparent reason, to ride quite close to the car in front, before gradually drifting back?…
Il car following è responsabile delle code a sinistra…
… You may have experienced this: Drivers seem reluctant to abandon the passing lane and join the lane of trucks chugging uphill, even when they are being pressured by other drivers, and even when the other lane is not crowded. What’s going on? Drivers may not want to give up the fast lane for fear of having trouble returning to it. They may also be unsure whether the person behind truly wants to go faster or is just keeping a tight space to prevent someone else from passing…
O del cosiddetto “sorpasso passivo”…
… One of the idiosyncrasies I have noticed in traffic flow is something I call “passive-aggressive passing.” You’re in the passing lane when suddenly the driver behind you pressures you to move into the slower right-hand lane. After you have done so, they then move into your lane, in front of you, and slow down, thus forcing you to pass them…
I blocchi non moltiplicano solo i ritardi ma anche i cambi di corsia: in vista di un blocco si corre a prendere la corsia reputata migliore.
La vicinanza delle altre auto, inoltre, ci spaventa e ci fa reagire in modo esagerato. E’ il problema degli innesti…
… A line of cars waiting to exit an off-ramp can trigger this same chain reaction, one study showed, even when all the other lanes were flowing nowhere near critical density…
Ma il vero problema dell’attrito si manifesta nei “colli di bottiglia”.
Sì, il problema dei colli di bottiglia non è il restringimento della strada – come molti credono - ma il problema dell’attrito.
Per capirlo giova l’analogia del riso:
… A simple way to see this in action involves rice. Take a liter of rice and pour it, all at once, through a funnel and into an empty beaker. Note how long it takes. Next, take the same rice and pour it not all at once but in a smooth, controlled flow, and time that process. Which liter of rice gets through more quickly?… Rice has more to do with traffic than you might think. Many people use water analogies when talking about traffic, because it’s a great way to describe concepts like volume and capacity…
L’imbuto ha sempre la stessa larghezza ma se noi ci rovesciamo dentro l’intera scatola di riso scorrerà meno velocemente rispetto ad un dosaggio alla fonte più moderato e costante. Perché?…
… The inflow of rice exceeds the capacity of the funnel opening. The system gets denser and denser. Particles spend more time touching one another. More rice touches more rice… Pouring less rice at a time—or moving fewer cars—keeps more space, and fewer interactions, between the grains…
Nel caso del riso si tratta di un attrito reale, nel caso delle auto di un attrito psicologico, il risultato non cambia.
Il problema dell’attrito fa sì che le rotonde funzionino meglio dei semafori…
… The “slower is faster” idea shows up often in traffic. The classic example concerns roundabouts… a properly designed roundabout can reduce delays by up to 65 percent over an intersection with traffic signals or stop signs. Sure, an individual driver who has a green light may fly through a signalized intersection much more quickly than through a roundabout. Roughly half the time, however, the light will not be green; and even if it is green there is often a rolling queue of vehicles just starting up from the previous red. Add to this such complications as left-turn arrows, which prevent the majority of drivers from moving, not to mention the “clearance phase,” that capacity-deadening moment when all lights must be red, to make sure everyone has cleared the intersection… The first cars in a queue squander an average of two seconds each, two seconds that would not have been lost had the car sailed through at the “saturation-flow” rate…
Le rotonde realizzano una velocità più regolare dei semafori neutralizzando i tempi di reazione. Oltretutto mantengono anche più alta l’attenzione.
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E’ curioso notare come in ogni parte del mondo ci si impieghi circa un’ora per arrivare sul posto di lavoro: dallo sperduto villaggio africano alla metropoli più intasata nulla cambia.
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Perché sono le donne a creare il traffico?
Perché prima non guidavano. Oggi si sono aggiunte al (poco) traffico che c’era un tempo…
… One striking thing the numbers seem to reveal is that women now make the largest contribution to congestion… Many of us can remember or envision a time when the typical commute involved Dad driving to the office while Mom took care… American families had only one car… in 1950 women made up 28 percent of the workforce. Today, that figure is 48 percent… you wouldn’t see these astonishing increases in traffic congestion in all indices of travel if women weren’t in the labor force, driving.”…
Niente donne, niente traffico.
Ma c’è un’altra ragione: prima si viaggiava quasi solo per andare al lavoro…
… In the 1950s, studies revealed that about 40 percent of daily trips per capita were “work trips.” Now the nationwide figure is roughly 16 percent.10 It’s not that people are making fewer trips to work but that they’re making so many other kinds of trips. What kinds of trips?…
Oggi si viaggia con altre motivazioni, specie il pomeriggio…
… Taking the kids to school or day care or soccer practice, eating out, picking up dry cleaning. In 1960, the average American drove 20.64 miles a day. By 2001, that figure was over 32 miles…
Si tratta di motivazioni che vedono impegnate soprattutto le donne.
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Come cerchiamo parcheggio?
Come parcheggiano le auto davanti all’Esselunga? Basta guardare posizionandosi lì la mattina…
… The next time you find yourself at a shopping mall or a store with a large parking lot where the store entrance more or less divides the lot in half by width, take a moment to observe how the cars are arrayed. Unless the lot is completely filled, you may be able to observe a common pattern. Chances are, the row that is dead opposite the store entrance will be the most filled, with cars stretching far out along the row. In each adjacent row, there are likely to be slightly fewer cars. This pattern will continue sequentially in each row so that if one were able to gaze down at the lot from above (as anyone can with Google Earth), the cluster of cars might look, depending on the lot’s occupancy, like a giant Christmas tree or, perhaps, like a bell….
Sostanzialmente i posti privilegiati sono quelli davanti all’ingresso.
Magari nelle file lontane ma davanti all’ingresso.
Parcheggiare un po’ a lato ma nella prima fila abbrevierebbe le distanze ma noi parcheggiamo davanti all’ingresso, anche se la fila è lontana.
Perché?
Perché inizialmente decidiamo di parcheggiare nel punto ottimo ottimo, ma poi, quando percorriamo una corsia del parcheggio decidiamo di parcheggiare nel punto ottimo di quella corsia.
Questa strategia ha un nome, si chiama “satisficing” e si contrappone alla strategia del “parcheggio ottimo”...
… The Nobel Prize–winning economist Herbert Simon has suggested, in a seminal theory he called “satisficing” (a mix of satisfying and suffice), that because it is so hard for humans to 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.”58 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…
E’ una strategia sviluppata andando a caccia. Oggi cerchiamo parcheggio ma un tempo cercavamo le prede da mettere sul fuoco.
E’ provato che chi parcheggia in posizione ottimale perde complessivamentepiù tempo (lo devo comunicare a mio suocero)…
… Whatever the case, something curious happens in parking lots. It seems that the people who actively look for the “best” parking place inevitably spend more total time getting to the store than those people who simply grab the first spot they see. This was the conclusion that Andrew Velkey, a psychology professor at Virginia’s Christopher Newport University, came to after he studied the behavior of parkers at a Wal-Mart in Mississippi…
Nelle strategie di parcheggio c’è un curioso gender gap…
… 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),51 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…
Ci sono parcheggiatori attivi (condor) e parcheggiatori passivi (gufi)…
… Velkey saw two kinds of behavior emerge: an active and a passive search strategy. Some people would drive around the lot looking for a space, 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 passive searchers, meanwhile, were like barn owls, perched and lying in wait… In our daily lives as parkers, we face these foraging questions. We must decide whether to act like condors or barn owls…
Chi vince? Dipende dagli orari, una strategia ottima non c’è. Il gufo va bene alla sera, quando la gente se ne va, il condor il giorno, quando la gente arriva.
Lo sapevate che 1/3 del traffico che vi fa bestemmiare in città è costituito da chi cerca parcheggio? Sappiatevelo…
… 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…
DONALD SHOUP è lo studioso che più ha insistito sui parcheggi a pagamento con tariffe di mercato.
Concordo: quando giro per i paesini liguri con i parcheggi gratuiti mi viene da prendere l’assessore e appenderlo.
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Più strade meno traffico?
No: spesso più strade, più traffico.
C’è una domanda latente di strade. Una domanda che si manifesta solo quando la nuova strada è costruita.
Il traffico è una bestia strana, una bestia con grande capacità di adattamento. Gli ingegneri del traffico hanno un motto “Venerdì sarà tutto normale”. Per dire, il Lunedì possono partire mille lavori, puo’ scatenarsi anche la rivoluzione del traffico urbano con i giornali locali che riportano tutto in prima pagina… ma per Venerdì sarà tutto normale.
Questa capacità di assorbire il negativo si manifesta purtroppo anche sul positivo.
Il dilemma di fondo è chiaro…
… 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”?…
Sentenza…
… studies suggest that induced travel is real… If you do not believe that new roads bring new drivers, consider what happens when roads are taken away…
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Ma c’è un altro modo attraverso cui la costruzione di una nuova strada puo’ essere dannosa….
… the Braess paradox…
Lo ha messo in luce il matematico tedesco Dietrich Braess. Cosa afferma?…
… 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 new drivers have been induced onto the roads)…
Come intuirlo?…
… 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 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… If you cannot improve your situation, why move to a different road?… 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… 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… 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 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.”…
Riassumendo: due autostrade: 1) la lenta sicura (1 ora di tempo); e 2) la veloce a rischio (1 ora di tempo se intasata, altrimenti 1/2 ora). Entrambe portano in città.
Ovviamente tutti scelgono 2) e arrivano in città in un’ora.
Postuliamo ora due autostrade siffatte: 3) la prima metà come 1 la seconda come 2 e 4) la prima metà come 2 la seconda come 1.
Quale prenderanno i pendolari per andare in città? E’ indifferente, tireranno la monetina e si distribuiranno in parti uguali sulle due autostrade. Tempo del viaggio? Un po’ meno di 1 ora poiché tutti percorreranno metà del percorso sulla 2 (veloce) e con traffico limitato.
Ammettiamo ora che tra la 3 e la 4 venga costruito un ponte a metà strada in modo da poter cambiare autostrada. Cosa succederà? Che a metà strada chi era su 4 passa su 3. I tempi medi aumentano. Risultato: una strada in più (il ponte) aumenta i tempi di percorrenza.
***
Come risolvere il problema del traffico?
Con i trasporti pubblici?
I pendolari sono entusiasti di questa soluzione:…
… 98% OF U.S. COMMUTERS FAVOR PUBLIC TRANSPORTATION FOR OTHERS —headline in the Onion…
Anche la risposta canonica: costruite più strade è fallata, lo abbiamo appena visto.
Non resta che il pedaggio…
… Later, the Nobel Prize–winning 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?42 (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.)43 Congestion charging, in cities like London and Stockholm, has been shown to work because it forces people to make a decision…
Il pedaggio vince sulla pigrizia…
… 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.”..
Da sempre c’è una città che insegna a tutte le altre: Disneyland…
… Early on, Disney realized that as the park grew in popularity, managing the queues of people would prove difficult, particularly on the marquee attractions like Space Mountain. What could you do? Disney could take the approach of our traffic networks, which is simply to let an inefficient kind of equilibrium take hold. Let people wait, and if the line is too long, they may decide on their own not to get in line (or get on the highway), and thus be diverted to other rides (roads). The queue will regulate itself…. Disney tried a form of congestion pricing. It issued ticket books in which the tickets’ values reflected the capacity of the rides. Popular rides like Space Mountain required E tickets, which were more expensive than A tickets, good for tamer attractions like the Horseless Carriage on Main Street. The idea was not only to prevent people from simply lining up for the top attractions but to spread people out across the park, avoiding traffic jams at places like Space Mountain… Disney finally hit upon the ultimate solution in 1999, when it introduced the FastPass, the system that gives the customer a ticket telling them when to show up at the ride. What FastPass essentially does is exploit the idea that networks function both in space and in time. Rather than waiting in line, the user waits in a “virtual queue,” in time rather than space, and can in the meantime move on to other, less crowded rides (or buy stuff). People can take a chance on the stand-by line, or they can have an assured short wait if they can simply hold off until their assigned time. Obviously, FastPass could not literally work on the highway. Drivers do not want to pull up to a tollbooth and be told, “Come back at two-thirty p.m.” But in principle, congestion pricing works the same way, by redirecting demand on the network in time…
Qualcuno propone: più informazione agli utenti delle strade!
Nooo, per carità, scatta il paradosso Onda Verde…
… Shreckenberg calls this the “self-destroying prognosis.” In his office at the University of Duisburg-Essen, he points to a highway map with its roads variously lit up in free-flowing green or clogged red. “The prognosis says that this road becomes worse in one hour,” he says. “Many people look at that and say, ‘Oh, don’t use the A3.’ Then they go somewhere else. The jam will not occur since everyone turned to another way. This is a problem.” These sorts of oscillations could happen with even short lags in information, in what Shreckenberg calls the “ping-pong effect.” Imagine there are two routes. Drivers are told that one is five minutes faster. Everyone shifts to that route. By the time the information is updated, the route that everyone got on is now five minutes slower. The other road now becomes faster, but it quickly succumbs to the same problem…
***
Il traffico è cultura. Avete mai guidato a Dehly in mezzo ai 48 tipi di autoveicoli?…
… “Delhi has forty-eight modes of transport, each struggling to occupy the same space on the carriageway. What other city is like this?”…
Un maelstrom motorizzato.
Una cacofonia di clacson che non smettono mai…
… They lurch, belch smoke, and ceaselessly toot their pressure horns….
Adesivi sui camion…
… “Horn Please” originally invited following drivers to honk if they wanted to pass the slower-moving, lane-hogging trucks on the narrower roads of the past, and I was told that it endures merely as a decorative tradition…
E laddove il traffico è più intenso, ecco comparire una vacca seduta tra le corsie…
… The most striking feature of Delhi traffic is the occasional presence of a cow or two, often lying idly in the median strip, feet away from traffic…
Difettucci dell’autista tipico di Dehly…
… Delhi drivers have a chronic tendency to stray between lanes, most alarmingly those flowing in the opposite direction… There are nearly 110 million traffic violations per day in Delhi…
Come si limitano gli incidenti in condizioni tanto estreme? Semplice, rendendo l’inatteso atteso. Tutti sanno che un’ Ape puo’ piombare sulla strada principale da una strada secondaria.
Quando sono stato a NY ho notato come i pedoni passino col rosso e attraversino fuori dalle strisce. A Copenaghen non succederebbe mai: il traffico è cultura. Un colpo di clacson a Roma ha significati diversi che a Stoccolma…
… It’s the reason a horn in Rome does not mean the same thing as a horn in Stockholm, why flashing your headlights at another driver is understood one way on the German autobahn and quite another way on the 405 in Los Angeles, why people jaywalk constantly in New York and hardly at all in Copenhagen…
Guarda al traffico e comprendi il grado di corruzione della città…
… In 1951, some 852 people were killed on the roads in China. In the United States in that year, 35,309 people were killed in traffic. In 1999, traffic fatalities in China had risen to nearly 84,000.31 The U.S. figure, meanwhile, was 41,508. The population of both countries had almost doubled in that time. Why did fatalities rise so much higher in China than in the United States? The answer lies in the number of vehicles in each country. In 1951, there were about 60,000 motor vehicles in China, while in the United States, there were roughly 49 million.32 By 1999, when China had 50 million vehicles, the United States had over 200 million—four times as many… What Smeed’s law showed was that, across a number of countries, ranging from the United States to New Zealand, the number of people killed on the roads tended to rise as the number of cars on the road began to rise—up to a point—and then, gradually if not totally uniformly, the fatality rates began to drop, as, generally, did the absolute numbers of fatalities… The nations that rank as the least corrupt—such countries as Finland, Norway, New Zealand, Sweden, and Singapore—are also the safest places in the world to drive…
Traffico caotico e incidenti mortali sono tipici dei paesi che si arricchiscono (legge di Smeed), si tratta proprio di quei paesi dove fiorisce la corruzione.
Traffico ordinato e incidenti in calo sono tipici dei paesi stagnanti. In questi paesi la corruzione percepita è minima.
***
Problema: noi non valutiamo bene i rischi della strada…
… Semiconscious Fear: How We Misunderstand the Risks of the Road…
Viaggiare in auto è un continuo calcolo del rischio…
… When we are in traffic, we all become on-the-fly risk analysts. We are endlessly having to make snap decisions in fragments of moments, about whether it is safe to turn in front of an oncoming car, about the right speed to travel on a curve, about how soon we should apply the brakes when we see a cluster of brake lights in the distance. We make these decisions not with some kind of mathematical probability in the back of our heads—I have a 97.5 percent chance of passing this car successfully—but with a complicated set of human tools…
Molte cose ci ingannano. Per esempio, i camionisti sembrano poco raccomandabili ma in realtà gli incidenti con i camion sono quasi sempre colpa degli automobilisti (che ci lasciano le penne)…
… In most cases, when cars and trucks collide, the car bears the greater share of what are called “contributory factors.” This was the surprising conclusion that Daniel Blower, a researcher at the University of Michigan Transport Research Institute, came to after sifting through two years’ worth of federal crash data… the reason trucks are dangerous seems to have more to do with the actions of car drivers…
L’istinto del rischi ci tradisce: il camion ci intimorisce e noi cambiamo corsia inutilmente…
… It was smart of the Detroit driver to feel risk from the truck next to him, but the instinctual fear response doesn’t always help us…
Quand’ero piccolo e andavo in vacanza in montagna ricordo i morti per “investimento di cervo”. mi dicevo “in effetti il cervo è un bestione”. Ora scopro l’arcano: quella gente è morta per aver tentato di evitare un cervo più che per averlo investito. Ha calcolato male il rischio: è più rischioso evitare che investire.
… In collisions between cars and deer, for example, the greatest risk to the driver comes in trying to avoid hitting the animal…
Per questo in molti luoghi di montagna campeggia il cartello…
… DON’T VEER WHEN YOU SEE A DEER…
Sulla strada non abbiamo feedback che ci dicono quanto rischiamo…
… This is why, it has been argued, it has long been difficult to convince people to drive in a safer manner. Each safe trip we take reinforces the image of a safe trip…
Ogni volta che arriviamo sani e salvi pensiamo “non è poi tanto rischioso”.
Eppure…
… “traffic fatalities are by far the most important contributor to the danger of leaving home.”…
Se non è rischioso guidare non è rischioso quasi niente!
Ma guidare non è sempre rischioso, ci sono alcuni momenti in cui è molto rischioso: il Sabato e la Domenica notte…
… In other words, just two nights accounted for a majority of the week’s deaths in that time period… fatal crashes occur much less often during rush hours… 8 of every 1,000 crashes that happened outside the peak hours were fatal, while during the rush hour the number dropped to 3 out of every 1,000… What’s so striking about the massive numbers of fatalities on weekend mornings is the fact that so few people are on the roads, and so many—estimates are as high as 25 percent—have been drinking…
Quanto multare l’ubriaco?…
… The economists Steven D. Levitt and Jack Porter have argued that legally drunk drivers between the hours of eight p.m. and five a.m. are thirteen times more likely than sober drivers to cause a fatal crash, and those with legally acceptable amounts of alcohol are seven times more likely. Of the 11,000 drunk-driving fatalities in the period they studied, the majority—8,000—were the drivers and the passengers, while 3,000 were other drivers (the vast majority of whom were sober). Levitt and Porter argue that the appropriate fine for drunk driving in the United States, tallying up the externalities that it causes, should be about $8,000…
E la velocità, come incide sui rischi?…
… The most important risk factor, one that is subtly implicated in all the others, is speed. In a crash, the risk of dying rises with speed…
La curva di Solomon…
… Solomon found after examining crash records on various sections of rural highway, seemed to follow a U-shaped curve: They were lowest for drivers traveling at the median speed and sloped upward for those going more or less than the median speed… “low speed drivers are more likely to be involved in accidents than relatively high speed drivers.”…
Chi va troppo veloce è un pericolo pubblico, ma anche chi va troppo lento: il vero pericolo sono i differenziali di velocità…
… It’s not the actual speed itself that’s the safety problem, they insist, it’s speed variance…
La gente calcola male i rischi. Che fare? Imporre? Imporre la cintura di sicurezza?
La soluzione ha un inconveniente: l’effetto Peltzman…
… the insides of cars have been made radically safer. In the United States (and most other places), fewer people in cars die or are injured now than in the 1960s, even though more people drive more miles. But in an oft-repeated pattern with safety devices from seat belts75 to air bags, the actual drop in fatalities did not live up to the early hopes…Were drivers trading a feeling of greater safety for more risk?… Describing what has since become known as the “Peltzman effect,” he argued that despite the fact that a host of new safety technologies—most notably, the seat belt—had become legally required in new cars, the roads were no safer. “Auto safety regulation,” he concluded, “has not affected the highway death rate.”… the increase in car safety had been “offset” by an increase in the fatality rate of people who did not benefit from the safety…
Siamo dominati dai comportamenti compensativi: se mi togli il rischio da una parte me lo prendo da un altra. Il mio rischio lo decido io.
Anche per questo la montagna di misure di sicurezza partorisce il topolino.
C’è poi un altro fattore: se metto una norma di sicurezza la rispetterà chi già guida in modo sicuro…
… This gap between expected and achieved safety results might be explained by another theory, one that turns the risk hypothesis rather on its head. This theory, known as “selective recruitment,” says that when a seat-belt law is passed, the pattern of drivers who switch from not wearing seat belts to wearing seat belts is decidedly not random. The people who will be first in line are likely to be those who are already the safest drivers…
Come capire se l’effetto Peltzman agisce anche su di voi…
… I have always considered the act of wearing my seat belt not so much an incentive to drive more riskily as a grim reminder of my own mortality (some in the car industry fought seat belts early on for this reason). This doesn’t mean I’m immune from behavioral adaptation. Even if I cannot imagine how the seat belt makes me act more riskily, I can easily imagine how my behavior would change if, for some reason, I was driving a car without seat belts…
Non guardare a come guidi quando i tuoi figli hanno seggiolino e cinture ma a come guidi quando non li hanno.
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Michael Wolf fotografa i pendolari di Tokyo.
