Archive for the ‘Traffic Psychology’ Category

To Wear Or Not to Wear (and Is That Even the Right Question?): Ian Walker on Cycle Helmets

When I was in the U.K. doing radio interviews for Traffic, I would often get asked if wearing cycle helmets actually made things less safe for cyclists. This happened primarily because the book features rather striking research by Ian Walker, a traffic psychologist at the University of Bath, and this was mentioned in the press kit.

To briefly summarize, in his study (published as “Drivers overtaking bicyclists: Objective data on the effects of riding position, helmet use, vehicle type and apparent gender,” in the journal Accident Analysis and Prevention), Walker outfitted a bike with a device that measured the distance of passing cars. He found, among other things, that drivers tended to pass more closely when he was wearing a helmet than when not (he was struck by vehicles twice, both while wearing a helmet).

This was a surprising, somewhat controversial finding that generated a lot of news coverage. To my mind, Walker’s findings were more interesting for what they said about interpersonal psychology on the road than safety itself; mostly because I felt, and Walker seems to agree, that the primary question of bicycle safety had less to do with the helmet than other factors. As the above photo suggests, cyclists in places like Copenhagen or Amsterdam very rarely wear helmets, and yet they enjoy a much safer ride than in places (like the U.S.) where helmet-wearing seems more ingrained. The argument is often made that those places have protected cycle lanes and the like — though the photo also shows that is not always the case.

But to return to the radio interviews, I often found myself getting frustrated because the radio journalists seemed to want a handy “takeaway” answer: Well, do helmets make cyclists safer or not? The problem was, I really didn’t know (disclaimer: I do wear one, rather out of habit and without much thought other than a fear of New York City streets).

This was a problem I had in trying to give many answers relating to traffic — there are often an endless series of “on the other hand” qualifiers. As with any kind of epidemiological inquiry, traffic presents such a complex system, with so many interacting variables (e.g., do helmets make drivers act less safe) and “confounding factors” and incomplete data sets, that coming up with easy answers is impossible: and anyone who seems to have easy answers probably doesn’t know what they’re talking about. One favorite example of this for me is the nutmeg you hear drivers say, with deeply held conviction: ‘Well I’ve heard it’s not speed itself that’s the problem, it’s differences in speed.’ This is a statement that is true — except when it isn’t. It lacks context, it lacks explanatory power. We would do as well, if not better, to note that every traffic fatality/injury involves speed: If the car wasn’t moving, no one would have died/been injured.

But I was curious as to how Ian Walker, after putting his research into the world and subsequently being asked these sorts of questions, undergoing these sorts of debates, ultimately felt himself about what his findings (at least on several stretches on English roads) had revealed.

Over to you, Dr. Walker:

“The apparently simple query ‘Do bicycle helmets work?’ turns out to be the most complex question I have ever encountered. Since I published my own small contribution to the nightmarish tangle of helmet research a couple of years ago, I have read and answered hundreds of emails on the subject from interested – in both senses of the word – people. I am grateful to Tom for giving me this chance to summarize a few of my disjointed thoughts on the matter.


Posted on Wednesday, October 1st, 2008 at 4:01 pm by: Tom Vanderbilt
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A Miracle of Controlled Chaos

Traffic is mentioned in an elegant paean to commuting in the Guardian by Joe Moran, author of the delightful Queuing for Beginners.

After first describing examining some of the hoary cultural critiques of commuting (“dragged out of sleep at six every morning, jolted about in suburban trains” and “tossed out at the end of the day into the entrance halls of railway stations, those cathedrals of departure for the hell of weekdays,” went one 1968 screed), Moran then goes on to wonder about the psychic value of the daily grind:

“The academic Eva Illouz invented the phrase “cold intimacies” to describe this culture in which emotional literacy is prized, pop psychology defines our identities, and our workplaces stress the importance of empathy and consensus.

We live in a world, Illouz writes, that is “Rousseauian with a vengeance”, in which our “emotions have become entities to be evaluated, inspected, discussed, bargained, quantified, and commodified”. Perhaps, then, we have learnt to welcome the commute as a neutral space where we can escape this obligation to be permanently available to others, and where an informal public life can flourish, without the emotional demands of work or home.”

Further, he notes, there is something to be marveled at in the sheer logistics of it all:

“Amid all the justified moaning about jams and delays, it is worth remembering that this rush-hour movement of 36 million Britons each day is really a miracle of controlled chaos. The National Travel Survey found that more than half of commuters, both in cars and public transport, have no problems with their daily journey. And even the large minority that do have problems generally arrive at work on time and in one piece, without murdering each other.”

He concludes with a curious detail:

“One of my students told me that in Second Life, that virtual world online, no one uses the roads or railways because they can simply teleport to their destinations. Nothing comes between the cyber-citizens and their real estate; commuting has been abolished. And part of me thought: what sort of life is that?”

Posted on Tuesday, September 30th, 2008 at 7:33 am by: Tom Vanderbilt
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Audi’s Dumb New Smart Technology

Do you remember how, in the early days of the personal computer, you would constantly hear of all the amazing things you could do with it, such wondrous tasks as “balancing your checkbook”? In other words, you were being asked to spend a significant sum to do something that would more easily and efficiently be done on the cheapest calculator.

I get something of that vibe — I’ll call it “egregious technology” — from a new Audi project called “Travolution” (thanks Jalopnik), which the company describes as such:

“Communications modules built into each traffic light are able to send messages to cars in the vicinity, alerting them to the time remaining until their next green phase. The car’s onboard system is then able to calculate the speed which the driver must maintain in order to pass through the light during this green phase, and displays this via the Multi Media Interface display.”

In other words, the traffic lights send a signal to the approaching Audi, which then gives the driver an approach speed that will allow them to fluidly sail through the intersection, avoiding fuel-wasting stops and starts.

I’m skeptical of this for a few reasons. The first is that my 2001 Volvo already happens to have this technology. What’s more, it cost me nothing to add it.

What’s the wonder device? My brain. Partially because I like to drive in a way that maximizes fuel efficiency, and partially because I don’t get much of a kick at idling at traffic lights, I tend to slow down ahead of time if I see I’m approaching an intersection whose traffic signal is red (conversely, and who doesn’t do this, if I see the green is “fading,” based on flashing ped signals, I will speed up, within reason).

I’m constantly astounded how often, in New York City, drivers — particularly taxi drivers — often blaze past me, only to find themselves lingering at the light (maybe it’s because we’re wired to focus on short-term gains). Then, even though I was going slower to begin with, but because I haven’t had to make a complete stop, I typically drive right past them.

Avoiding unnecessary stopping and acceleration is one of the main precepts of “eco-driving” or “hyper-miling,” but it’s really just a function of being an alert, thinking driver (and some studies have noted the connection between fuel efficient driving and safe driving).

This leads me to my second big complaint with Audi’s system. Not only is it asking the driver to take their eyes off the road to look at a gauge to get information they could more or less discern by looking ahead, at the road, it presumably wouldn’t know things like the length of the queue of vehicles waiting at the light (unless, perhaps, they were all Audis) — so any stated approach speed might be completely inappropriate given the necessary start-up and clearance time of all the other vehicles. The simple fact of being given an approach speed for the intersection might induce some kind of “automatic” thinking, in which a driver may focus on maintaining the correct speed as their key task rather scanning the intersection (where close to half of all crashes occur) — in the way drivers can focus too much on the light itself rather than, say, vehicles that haven’t cleared the intersection for some reason.

Of course, being given the correct approach speed for hitting the green isn’t much help if you’re asked to approach at five miles an hour because the light is backed up with traffic. That’s why I suspect the money (not sure what Audi’s communicative lights would cost) would be better spent on lights that could talk to each other. Which we already have, of course, in some places — but even these need human help once in a while.

Posted on Thursday, September 25th, 2008 at 1:32 pm by: Tom Vanderbilt
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Did You See the Way That Car Looked at Me?

Have you ever felt particularly menaced (or amused) by an approaching car as you crossed in a crosswalk, or as you looked up to see it in the rear-view mirror of your own car? Did you ever think it might be because it felt, strangely, as if an angry (or happy) face was looking at you? Would this alter the way you behaved toward the vehicle?

In a new paper by Sonja Windhager, et al., “Face to Face: The Perception of Automotive Design,” published in the latest issue of Human Nature, the authors, working from the idea that evolution has primed us to be extremely sensitive to the human face (drawing key inferences after a mere 100 ms), wonder if we might not draw similar information from inanimate objects — like cars — that just happen to have seemingly facial features.

Posted on Tuesday, September 23rd, 2008 at 3:54 pm by: Tom Vanderbilt
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All Over in the Blink of an Eye (but Not the Mind’s Eye)

From The Age newspaper in Australia, via, comes this surprising, sobering “anatomy of a crash,” the car in question being the 5-star Ford Falcon (the one made in Australia, not the one your father had when he was young).

The article leads by noting: “Survivors of serious car crashes often say time appears to slow down in the moments around the impact and that they can recall the event in extraordinary detail.” (and somehow the images we always see of crash-test dummies in slow motion tends to reinforce that).

But an actual reconstruction of the events shows the sort of reshuffling of the deck the brain is playing with memory:

“This is a reconstruction of a crash involving a stationary Ford Falcon XT sedan being struck in the driver’s door by another vehicle travelling at 50 km/h.

One millisecond equals 1/1000th of a second.
0 milliseconds – An external object touches the driver’s door.
1 ms – The car’s door pressure sensor detects a pressure wave.
2 ms – An acceleration sensor in the C-pillar behind the rear door also detects a crash event.
2.5 ms – A sensor in the car’s centre detects crash vibrations.
5 ms – Car’s crash computer checks for insignificant crash events, such as a shopping trolley impact or incidental contact. It is still working out the severity of the crash. Door intrusion structure begins to absorb energy.
6.5 ms – Door pressure sensor registers peak pressures.
7 ms – Crash computer confirms a serious crash and calculates its actions.
8 ms – Computer sends a “fire” signal to side airbag. Meanwhile, B-pillar begins to crumple inwards and energy begins to transfer into cross-car load path beneath the occupant.
8.5 ms – Side airbag system fires.
15 ms – Roof begins to absorb part of the impact. Airbag bursts through seat foam and begins to fill.
17 ms – Cross-car load path and structure under rear seat reach maximum load.
Airbag covers occupant’s chest and begins to push the shoulder away from impact zone.
20 ms – Door and B-pillar begin to push on front seat. Airbag begins to push occupant’s chest away from the impact.
27 ms – Impact velocity has halved from 50 km/h to 23.5 km/h. A “pusher block” in the seat moves occupant’s pelvis away from impact zone. Airbag starts controlled deflation.
30 ms – The Falcon has absorbed all crash energy. Airbag remains in place. For a brief moment, occupant experiences maximum force equal to 12 times the force of gravity.
45 ms – Occupant and airbag move together with deforming side structure.
50 ms – Crash computer unlocks car’s doors. Passenger safety cell begins to rebound, pushing doors away from occupant.
70 ms – Airbag continues to deflate. Occupant moves back towards middle of car.
Engineers classify crash as “complete”.
150-300 ms – Occupant becomes aware of collision.”

What’s fascinating about all this is not simply the rapid fire technology at work (I’m still trying to deal with that computer deciding whether it was a shopping trolley or another car that has struck), but how much has gone on before we even register it — and this at 50 km (31 mph), so you can imagine what’s happening at higher speeds — even though in our subsequent reconstruction of events we may have imagined that time actually slowed down the during the event.

I couldn’t help but think of the work of David Eagleman, of the Baylor College of Medicine, in this regard. In his paper “Does Time Really Slow During a Frightening Event?”, Eagleman, through some clever techniques involving a (somewhat paradoxical) “controlled free-fall system,” found that rather than time actually slowing, a la the fight scenes in The Matrix, what seems to be going on, the researchers speculated, is “that the involvement of the amygdala in emotional memory may lead to dilated duration judgments retrospectively, due to a richer, and perhaps secondary encoding of the memories. Upon later readout, such highly salient events may be erroneously interpreted to have spanned a greater period of time.”

In other words, because of the nature of the event, people may have had, essentially, more of a memory of it, so when they later thought of it, it took longer to “replay.” But in the case of the Falcon, the event was essentially over before the driver would have realized what was happening.

Posted on Tuesday, September 16th, 2008 at 4:04 pm by: Tom Vanderbilt
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“The Whole Village Has Become More Human”

An alert reader sends along some more coverage, this time by Isabelle de Pommereau in the Christian Science Monitor, of Bohmte, a German village that has become another waypoint in the evolving “Shared Space” movement (I was in the town a few years ago, for a Shared Space conference, but haven’t been back since things were changed). The town, like many, felt overwhelmed by the 13,000 vehicles per day coursing through its small center.

Readers of the book and blog by now may well know the drill:

“But this summer the town reworked its downtown thoroughfare, not only scrapping the traffic lights but also tearing down the curbs and erasing marked crosswalks. The busiest part of the main street turned into a “naked” square shared equally by bikes, pedestrians, cars, and trucks. Now, there is only one rule: Always give way to the person on the right.”

Bohmte is providing yet another surprising example of the types of environments in which this sort of thing can be done: “What’s revolutionary about Bohmte is that it took off its signs on a state highway with a lot of traffic,” says Heiner Monheim, a traffic management expert at the University of Trier, speaking at a recent European conference on sign-free towns convened here. Beyond that, Monheim says, the model’s real legacy is to have brought people closer to “rediscovering and appreciating cities not only as traffic places but also as human, social places.”

But I was also struck in particular by this passage:

“Two months into the experiment, ‘Instead of thinking, ‘It’s going to be red, I need to give gas, people have to slow down, to look to the right and the left, to be considerate,’ says Ms. Rubcic… The bonus? Town people recognize they have become a bit closer to one another. ‘The whole village has become more human. We look at each other, we greet each other,’ she says.”

Posted on Tuesday, September 16th, 2008 at 3:23 pm by: Tom Vanderbilt
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How’s Our Driving?

I was intrigued by the conceptual art piece pictured above, Luther Thie’s LA Interchange, which I read about recently via BldgBlog.

The piece, which would sit at the intersection of the Santa Monica and Harbor Freeways, “uses real-time automobile accident information culled from the California Highway Patrol Incident Report website and would activate the enormous water fountain at the intersection of the freeways. Visitors on location at the park would also see a digital display streaming from the CHP website (location/region, date, time, accident type and status). This real-time data display system creates a real-time memorial to California highway accident victims. Highway activity can be viewed as a kind of “life-pulse” of the State transportation system. The fountain is, in a sense, the heart of the roadway system, reacting to the endless accident events on the highways. When a fatality occurs, the fountain rises to its highest possible point and blue lights illuminate the water feature, evoking a sublime moment of reflection for the spectators.”

This idea put me in mind of several things. First, the fountains at the laweiplein in Drachten, in the Netherlands, home of the famous un-signed “squareabout” pictured below. These water levels rise with congestion, however, not fatalities.

More directly, however, it reminded me of something I had seen in Hanoi, Vietnam, in the busy intersection near the Daewoo Hotel off of Kim Ma Street: A giant billboard (pictured below), sort of Fenway Park meets Socialist Realism, one section of which reported ongoing road fatalities (and thanks to Greig Craft at the nearby Asia Injury Prevention Foundation for pointing this out to me). It’s not quite visible in this shot, but there are categories like “traffic fatalities this year,” “today,” etc. — as well as time and temperature.

It’s an interesting idea, and one that I’ve not seen replicated anywhere else. It recalls the sort of factory-floor safety campaign signs one sees (“X days since accident”), depicting information that we generally don’t have access to as we drive — feedback if you will (and apparently this has been tried at least one other place, as the photo below shows). I’m not sure to what extent this would change behavior, or what people would draw from the information, but as it now stands the only way we are reminded of the danger of the road is the impromptu roadside memorials (or “ghost bikes”) that are erected (and typically removed by highway departments). But I’ve often wondered if leaving those memorials up would be more effective than other traditional warning signs, in terms of influencing behavior.

Posted on Thursday, August 21st, 2008 at 9:37 am by: Tom Vanderbilt
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The Politics of Late Merging?

My favorite letter in response to the New York Times Magazine Cynthia Gorney merging piece (in which I’m mentioned) was this one, from Mike Adamsky in Mendham, N.J.:

“Oh, my goodness, if Gorney’s article isn’t a perfect political allegory, I don’t know what is. Gorney is the classic Democrat, fretting about power balances and whether or not someone is getting ahead “unfairly.” She rails against the sidezoomers, even though experts have told her that utilization of all lanes is the most efficient mode. She’s probably also on the side of repealing the so-called “Bush tax cuts” even though some analysts say that these “cuts” resulted in a greater proportion of overall taxes being paid from the high-income group.

Padilla, the operations worker, is the classic Republican. He sees the opening and seizes the opportunity. Is this fair? He thinks so. The open lane that allows him to get ahead is equally available to everyone. He probably supports drilling in the Arctic National Wildlife Refuge. Why? Because he wants cheaper gas, and we’ve got it sitting right there!

Morgan, the cop, is the classic libertarian. We’ve got enough rules governing behavior already. The sidezoomer is fully entitled to try to cut, the lineupper is fully entitled to try to keep him out. No blood, no foul. Morgan stays the heck out of the vast majority of interactions. Let the games begin.

Fortunately, Gorney does show us how it’s supposed to work: we all just have to learn to behave like ants — productive little creatures who don’t brood or waste energy pounding dashboards.”

Given my own conversion to late merging, I wondered what this said about my own politics. Creeping Republicanism? Well, actually, the system I advocate is the one tried by engineers in which merging instructions are carefully and precisely laid out (thus allaying feelings of wronged social justice), perhaps even backed by enforcement. So I suppose this makes me a sort of Scandinavian Social Democrat, vis a vis using “big,” rational government planning to engineer effective (yet fair) social outcomes.

One is tempted to pursue the potential implications of the politics of merging. Would there be, say, a communist merging scheme? (wealthier cars are sent back to the end of the line in favor of rusty Ladas) A fundamentalist Right stratagem? (whatever lane you are in is God’s will) Anarcho-syndacalist merging, anyone?

Posted on Tuesday, August 19th, 2008 at 7:25 am by: Tom Vanderbilt
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Calling Dan Ariely

From today’s New York Times, about growing inventories of used SUVs on car lots. I’m not quite sure what psychologists would call this — perhaps a focusing effect?

“Given how much the automakers and dealers are willing to knock off an S.U.V.’s price, this is not a bad time to buy one, said Jesse Toprak, the director of industry analysis at Edmunds. Yet so many consumers are eager to avoid weekly $100 fill-ups that they are more focused on saving money at the gas pump than at the dealership.

“It’s a very psychological decision,” Mr. Toprak said. “You pay for the car just once, but you go to the pump every week, so that almost seems more important to you. Every time you go to the pump, you just want to feel good about it.”

And so thousands of Americans have been exchanging their sport utility vehicles for fuel-efficient cars, despite low trade-in values for the larger vehicles and a scarcity of small cars that has allowed dealers to charge sticker price or more for them.

“When you trade in a large S.U.V. for a compact car, you’re selling low and buying high,” Mr. Toprak said. “For a lot of people that’s not really logical, but they’re not really running the numbers.”

The story after the jump… (more…)

Posted on Wednesday, August 13th, 2008 at 4:22 pm by: Tom Vanderbilt
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Shut Up and Drive

Often when I’m driving, I find myself entering a difficult situation — a tricky lane-change, an unfamiliar turn — and I’ll actually ask my passenger (typically my wife) to essentially stop talking for a moment (or they will voluntarily do so) as the situation resolves itself. This, of course, is one of the major problems with talking on a cell phone versus talking with a passenger: Not only are they providing another set of helping eyes, but they can sense when would be good for them to modulate their conversation in some way, whereas the person on the other end of the cell-phone will seemingly keep droning on, taking away from the driver’s workload.

This point, fairly well established by now, is made again in a new study (PDF here) by Samuel G. Charlton, University of Waikato, Hamilton, for Land Transport New Zealand. The study, as others have, found that drivers on cell phones had slower reaction times — yet drove at higher average speeds — than drivers with passengers as they went through a number of hazards in a driving simulator. Interestingly, this study also featured a person on a cell-phone who was not present in the car yet had access to the driver’s view, so they have a passenger-like view of the road.

The key to performance seemed to be what the paper calls “conversation suppression,” i.e., knowing when to shut up: “Passengers talking to drivers made shorter utterances, had more frequent pauses and were more likely to be talking about the upcoming hazard than cellphone conversors. Drivers and their cellphone conversors tended to make longer utterances than the other participants, were less likely to mention the hazards, had the poorest recall of the hazards, and had the highest crash rate.” Even when the remote cell phone conversor had access to the driving scene, they didn’t tend to adjust their conversation as much as the passenger did — maybe there’s just something ineluctable in actually being there.

The study includes one other interesting, but to my mind a bit strange, finding. Drivers did a bit better on the cell phone when an automated hazard alert message “beeped through” their call, alerting them to some upcoming traffic hazard. This gave the driver the necessary cue to break off the conversation a bit. These alerts would presumably be triggered by some sort of beacons in the road infrastructure, particularly at hazardous points. But, of course, the thing about driving is one never knows when it’s going to become hazardous, and it certainly isn’t always at the accident “black spots” (which are often just statistical aberrations in any case). There are innumerable issues here, from a driver’s over-reliance on the hazard warning system, to the idea that they may be brought back “into the loop” with not enough time to react and not enough knowledge of the situation.

Posted on Tuesday, August 12th, 2008 at 9:34 pm by: Tom Vanderbilt
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The Caldecott Tunnel Problem

I recently met a kindred spirit, on the other coast, who had been stewing over a type of problem similar to that which had launched my own multi-year investigation into the strange social dynamics of traffic: Merging.

Cynthia Gorney, who teaches at the University of California-Berkeley journalism school and writes for National Geographic and many other places (this after an award-winning career at the Washington Post), kept stumbling upon a daily drama at the Caldecott Tunnel, in Northern California (pictured above). There were people who would dutifully line up on the narrow approach the tunnel entrance, and then people who would “sidezoom” along a frontage road, veering back into the active lane at the last moment. The whole thing is described in her insightful, and very funny New York Times Magazine article today, titled “The Urge to Merge.”

Her merging problem is a distinct problem from the “early” and “late” merge I describe in my book, which in the specific case I was discussing only relates to construction work zone merges in which two lanes are dropping to one, and signage warns something like “merge right, one mile.” Caldecott, as far as I can surmise, as I haven’t experienced it myself, is a strange situation; one, because unlike a temporary construction zone situation, the same thing repeats itself every day at Caldecott — the dilemma is built into the very landscape — and much of the traffic on it is presumably daily commuters (and indeed, an “evolutionary stable strategy” appears to have taken hold by which, according to Gorney’s reckoning, two-thirds of people line up and one-third side zoom). Two, the lane that the side-zoomers are using isn’t technically, as in my situation, a lane that was going to become inactive (and thus the people using it as a sort of merging reservoir weren’t holding up traffic going elsewhere). It is spare capacity to the extent the frontage road is not used very often, but then one wonders if it should just be turned into a de facto merging bay, and marked accordingly. Rather than stigmatizing “cheaters” and upsetting the prevailing order, this would institutionalize the practice, thus, presumably, easing the social tensions.

But the fact that the geometries and psychologies of Gorney’s own merge problem could yield a long article, full of interesting traffic tidbits and theories, speaks to the complexities of traffic. Merging prescriptions, it seems to me, are like medicine: Use only where directed (and watch out for side effects). The people in New York who use an active lane to drive to the front of the queue on the FDR to jump onto the onramp for the Brooklyn Bridge (dangerously stopping for a moment in the middle of that active lane, forcing everyone in their lane to then merge left, at relatively high speeds) should receive a good old-fashioned Singaporean caning, IMHO.

And of course it’s really just more than merging at stake here. These sorts of tensions strike right to the heart of American culture. Gorney found herself musing at the merge point, “this is the problem with modern American capitalism, really, this anti-aristocratic all-men-are-created-equal narrative we pretend to cherish while simultaneously celebrating the individual’s right to do whatever advances his own interests without technically breaking the law.” I think something similar may underlie the left-lane-is-for-faster-traffic dynamic on U.S. roads: It’s a good idea in practice, but someone’s always going to want to go faster, and that person’s rights are going to mash up against the guy who’s already going pretty damn fast, is exiting on the left soon anyway, and thinks he also has a right to be in the lane he’s in.

I later emailed Gorney a fragment I had come across in Robert Axelrod’s classic The Evolution of Cooperation, talking about experimental war games and strategy: “When the players will never meet again, the strategy of defection is the only stable strategy.” Isn’t this really the heart of traffic — there’s little incentive for doing the right thing when your good deed won’t be recorded in future rounds by your fellow game players. Perhaps, as the WOPR computer put it in that classic of 80s geekdom War Games, “the only winning move is not to play.”

In any case, I recommend the article highly, and not just because it contains the words “Vanderbilt’s book is terrific…” Follow the link or check out the text after the jump, and Happy merging!

Posted on Sunday, August 3rd, 2008 at 8:04 am by: Tom Vanderbilt
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Passengers Are Good For You

Amidst all the talk of ABS, ESC, and smart headlights that follow curving roads comes a reminder of a simpler in-car safety device: Passengers.

As Chris Lee and Mohamed Abdel-Aty, in the civil engineering departments of the University of Windsor and the University of Central Florida, respectively, report in a paper forthcoming in Accident Analysis & Prevention, drivers who had passengers in their cars were less likely to be involved in a crash.

They reached this conclusion after studying five years’ worth of crash data, linked to inductive loop readings, for a stretch of Interstate 4 in Orlando, Florida, picking out random involved drivers from crashes. Among 2817 crashes, 62% drove alone and 38% carried passengers (I know you’re thinking that more people drive alone so why wouldn’t there more be crashes by single drivers, but as a way to estimate exposure they used the sample of non-cited drivers). There’s all sorts of interesting observations here (drivers who were alcohol-impaired tended not to have passengers), drivers who had passengers seemed to wear seat-belts more often, and also that crashes tended to be less severe among cars having passengers (which may indicate a heightened sense of caution due to the responsibility of having other people in the car; they do caution they’re unable to state the speed of other crash-involved vehicles not chosen in sampling).

The argument has been raised that passengers serve as a distraction for drivers, but these findings add further evidence to the pro-passenger side: Passengers not only act as a second set of eyes, they help keep us awake, provide feedback to potential safety gaps in our own driving (what you might call a ‘backseat driver’), and may increase our sense of responsibility on the road. All these seemingly balance out or overcome the potential distractions they may cause.

The big exception here, of course, is teens, whose crash risk tends to increase with each passenger of a similar age.

Posted on Monday, July 28th, 2008 at 2:28 pm by: Tom Vanderbilt
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The Trouble with Traffic School

Unlike Nicole Richie, I’ve never been to traffic school, that strange institution, found particularly in California, where errant drivers go as penance for DUIs (e.g., Richie) and other offenses and, rather bizarrely, to get points and convictions taken off your license (if only there was a “burglary school” for thieves who wanted to remove some blemishes from their criminal record). I don’t know if they’re anything like this skit, but the sense I’ve always gotten from visiting the websites (for “Improv Traffic School” or “Singles Traffic School”) and reading some of the articles , is that they’re light on actual education and filled with bored people merely trying to lower their insurance rates.

The question is: Are people really learning anything in these schools? Are they capable of learning something? In their excellent book Mistakes Were Made, psychologists Carol Tavris and Elliot Aronson tell an interesting story about a traffic school: “As participants went around the room, reporting the violations that had brought them there, a miraculous coincidence occurred: Not one of them was responsible for breaking the law. They all had justifications for why they were speeding, had ignored a stop sign, ran a red light, or made an illegal U-turn.” People seemed unable to overcome the “cognitive dissonance” between their image of themselves as a good driver and the fact they had done something stupid or illegal.

A new study (via IIHS) by Michael Gebers of the California DMV, titled “A traffic safety evaluation of California’s traffic violator school citation dismissal policy,” updating earlier research, shows that traffic schools seem to have an unintended consequence: They raise a driver’s crash risk.

As IIHS notes, “despite their lower initial crash risk, traffic school drivers had a crash rate about 5 percent higher than that of convicted drivers during the year following the citation.” There are other problems: The policy of removing points and convictions from a driver’s record “reduces the ability to predict, or calibrate, the future accident expectancies” of those drivers by masking their true driving record. By lowering those drivers’ insurance rates, some drivers without convictions may actually end up paying more, subsidizing the would-be Nicole Richies of the world (some 1.2 million drivers’ citations are dismissed this way every year). Strangely, the DMV itself has called for the schools to be “abolished” or greatly restricted (and if “traffic schools” were to exist, shouldn’t the DMV itself be running them?)

The study reminded me of another, in The Lancet, by Donald Redelmeier, Robert Tibsharani, and Leonard Evans, which found that receiving a conviction for a traffic offense was something of a life-saver: “The risk of a fatal crash in the month after a conviction was about 35% lower than in a comparable month with no conviction for the same driver.” (the effect dropped after that).

Convictions, after all, are a form of feedback, however inexact, pointing out a driver’s mistakes, inducing caution. How does knowing these can be rinsed off of one’s record do anyone any good? I’d like to hear from any pro-traffic school people, or indeed stories from any traffic school attendees.

Posted on Thursday, July 24th, 2008 at 11:52 am by: Tom Vanderbilt
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Murder at the Traffic Circle

I wasn’t quite sure what could top, in terms of senseless road depravity, the story, from Los Angeles, of the driver who attacked a pair of cyclists with his car (it was his second reported altercation).

But then I read about the case of the Seattle man who was killed while tending to the flowers in the traffic circle outside his house, apparently by some passing drivers who took issue with the safety cones he had temporarily put up while watering. The man, a Vietnam vet, had himself lobbied for the circle after a car had struck his house.

Posted on Wednesday, July 16th, 2008 at 7:49 am by: Tom Vanderbilt
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Mind-bending Illusions on LSD

The recent discussion in the press of illusory speed bumps in Philadelphia reminded me of a conversation I had a while back with the Chicago Department of Transportation. For years, the curve at Oak Street on Lake Shore Drive has been something of a crash hot-spot. It’s within the typical engineering guidance for acceptable curves, but given that drivers on LSD tend to treat the Drive as an urban expressway rather than the boulevard it really should be, there’s been a consistent crash problem, particularly on rainy days and the like.

CDOT responded with a series of gradual alterations. They made the lane markings more distinct. They made the curve warning signs bigger. Then they added flashing lights. Drivers still weren’t getting the message. So CDOT got perceptual. (more…)

Posted on Monday, July 14th, 2008 at 2:17 pm by: Tom Vanderbilt
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On “Distracting Miss Daisy”

A few readers have asked me what I thought of “Distracting Miss Daisy,” an article by Duke University psychologist John Staddon in the current Atlantic (the full text is past the jump).

To briefly summarize, Staddon, who has driven in both the U.K. and the U.S., thinks American drivers suffer from a surfeit of traffic signs and speed limits. “The more you look for signs, for police, and at your speedometer, the less attentive you will be to traffic conditions.” He argues this helps explain the superior traffic safety record of the U.K.

On the whole, I was quite sympathetic to the spirit of the article, which was lively and well-argued — indeed, it visits a number of themes and places mentioned in my book (which has, for example, a section called “The Trouble with Traffic Signs”). His line, “we spend a lifetime on the roads after we get our licenses, and we’re being trained by our experiences every day,” could serve as a summary of Traffic. And as someone who recently took, as an experiment, a U.K. driving test (I’m writing an article about this), I’ve got my own opinions about comparative driving culture in the U.S. and the U.K., some of which are in line with Staddon’s point of view.

There were a few points in the article I thought deserved discussion, however.

1.) He says that in his experience, people “drive faster” in Britain. This just shows, I suppose, how subjective experience is. I challenge anyone to spend a week taking black cabs in London, and a week taking Yellow Cabs in New York City, and report a higher average velocity in the former. Also, the default speed limit in England of “lit, urban roads” is 30 mph. I’ve been in U.S. cities, in fairly urbanized areas, with (unobeyed) 40 mph limits. While we’re on the subject of limits, he does not mention in his piece the widespread deployment of speed cameras and red-light cameras in the U.K., two technologies which would seem “designed to control drivers and reduce their discretion” — a charge he makes against U.S. traffic safety efforts.

2.) He rightly invokes “risk compensation” in discussing why safety improvements in cars do not often produce the desired results: The safer people feel, the more riskily they act. But a bit later, he notes, “a particularly vexing aspect of the U.S. policy is that speed limits seem to be enforced more when speeding is safe.” (e.g., a sunny day). But is this not a form of risk compensation in itself? After all, most crashes occur during the day, during normal weather — the times we no doubt feel safer. As Leonard Evans notes in Traffic Safety, nearly 85% of fatal crashes happen on dry roads. There’s no such objective, quantifiable thing as a “safe” speed in traffic — plenty of people have died driving at the proper “design speed” of roads, while many children have been killed in driveways by cars going under 5 mph. The only thing we scientifically know is the higher the speed at which you collide with something, the greater the physical damage, and greater the risk of dying.

3.) And on the subject of speed, I am skeptical of Haddon’s claim that “looking at your speedometer” is an important form of distraction on the roads. First, I’m not sure how much time is actually spent looking at speedometers (in one study, drivers were asked, after they went through a slow school zone, how fast they were driving, and their estimates were wildly low). The second is that experienced drivers typically have a lot of spare cognitive workload, plenty for quick glances at gauges — and any minor distraction from a speedometer pales with the demands of, say, cell-phone conversations.

4.) I was interested that he notes that he finds roads “generally wider” here, which one might think would make things safer. In my U.K. driving test, taken in suburban London, I was quite surprised to find how often, on small residential streets, I had to pull over to let another car by. In general, I found road geometries tighter (and I was driving a fairly small car). But this is one of the ongoing debates in traffic safety: Making roads wider means you have less chance to bump into someone, but it also means you’re likely to drive faster. The experiments in which traffic control have been taken away (e.g., Drachten, Poundbury) only work because they are happening at very slow speeds, where the logic of human interaction, and not traffic engineering, take over.


Posted on Thursday, July 10th, 2008 at 10:11 am by: Tom Vanderbilt
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The MPH Illusion: How We Misjudge Time Savings on the Road

Imagine there were two roads that could be fixed to improve drivers’ travel times. Imagine also they’re the same length, but have different average speeds.

Fixing the first road will see drivers’ speeds increase from 40 kph to 50 kph.

Fixing the second road, meanwhile, will see drivers’ speeds go from 80 kph to 130 kph.

Given that the construction costs would be the same to fix each road, which road would you choose to improve? Which would result in more time saved (and, hence, more social benefit)?

If you’re a regular, math-challenged sort like me, you probably picked the second option. But apart from some minor rounding differences, the amount of time saved for each is actually the same.

This example comes from a fascinating new paper, “Driving Speed Changes and Subjective Estimate of Time Savings, Accident Risks and Braking,” by Ola Svenson, head of the Risk Analysis, Social and Decision Research Unit at Stockholm University.

I’m admittedly someone who has trouble computing things like how much time an increase in speed will save — once you get me off the nice 60 mph mark (a mile a minute), things get a little fuzzy. But now I’ve found I’m apparently not alone. When Svenson asked this to a group of respondents, a majority thought the 80 to 120 kph option was better. The reason, he speculates, has to do with a sort of “proportion heuristic,” an effect that’s been found in many other contexts (the work of Daniel Bartells is instructive here); in what he calls a “ratio rule,” we’re biased by the ratios in speed changes, rather than employing the actual, more complex formula.

What this means on the road is that we may underestimate time savings of increases in lower speeds and, perhaps more importantly, overestimate the time savings we gain when we begin to accelerate from an already high speed. He also looked at estimations of crash risk and braking distance as it applies to speed — both of which are non-linear — and found similar mis-estimations. He notes: “Intuitive arguments for higher speeds may be biased.”

Astute readers will note the curious echo here of another study, the so-called MPG illusion, by Duke University researchers Richard P. Larrick and Jack B. Soll, which found that increases in MPG from 16 to 20 can save as much fuel, relatively, as going from 33 to 50 mpg.

Previous research has found that we tend to overestimate trip lengths, and we think the waits at things like traffic lights were longer than they really were. The lesson in Svenson’s new paper, I suppose, is that that a car’s instrument panel is more complicated than it appears.

Posted on Tuesday, July 8th, 2008 at 3:50 pm by: Tom Vanderbilt
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The Curious Psychology of Bumper Stickers

While I was out of the country, a new study on bumper stickers was hitting the media. As it touches upon on a number of things discussed in Traffic, the study, “Territorial Markings as a Predictor of Driver Aggression and Road Rage,” by William J. Szlemko, Jacob A. Benfield, Paul A. Bell, Jerry L. Deffenbacher, and Lucy Troup, all of Colorado State University, was right up my alley.

The study, published in the June issue of the Journal of Applied Social Psychology, essentially seeks to explain what part of aggressive driving behavior might be caused by the very environment of traffic, and the way we understand it and inhabit it. Working partly from a previous theory (i.e., I. Altman, The Environment and Social Behavior), the authors delineate the different types of space we inhabit: Primary, Secondary, and Public. A primary territory would be one’s home; a secondary would be a space one inhabits temporarily (the office); while public territory would be a park bench. One interesting source of tension noted by Altman is when one type of space (primary) is adjacent to another (public). When these are adjacent, “the potential for miscommunication and conflict increases as a result of confusion of social norms for each territory type.”

This is exactly the kind of situation we have in traffic: We sit in our own cars, occasionally acting like they are rooms closed off from the rest of the world; but most of the time we drive, save for our own garage, we drive in a public setting. As the authors note, however, some “boundary confusion” exists: “How many times have drivers uttered the phrase ‘He just got into my lane?’ ”

If one of the hallmarks of primary space is a tendency to mark it in some way, to define one’s territory, the authors speculated, then the opportunity for boundary confusion might be highest among those most committed to marking territoriality over their primary space. Thus, they argued, people who personalized their vehicles, and reported showing the most attachment to their vehicles, would act most aggressively to defend their territory in the transitional spaces of traffic.

And this is precisely what they found, in a self-reported survey of college students: “Both number of territory markers (e.g., bumper stickers, decals) and attachment to the vehicle were significant predictors of aggressive driving.”

While I found the study novel in its approach, and its implications fascinating, I was left with a few questions. (more…)

Posted on Monday, June 30th, 2008 at 1:55 pm by: Tom Vanderbilt
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Don’t Just Drive Less. Drive Smarter.

I’ve got a very short piece in today’s New York Times, part of a roundup of writers responding to high fuel prices.

Studies have shown significant increases in fuel economy are achievable simply by changes in driving style (a few things got cut from this piece, by the way, including an obvious one: Cruise control aids MPG — but not cruise control at 70 mph).

One question, of course, is exactly how much a price increase is necessary to spur changes — not to mention those changes are tough to measure. But an interesting study (download PDF) by Kara Kockelman and Matthew Bomberg of the University of Texas of drivers in Austin, Tx., during the 2005 gas price spike reported: “Adjustments in style of driving also appear to be a viable strategy of coping with high gas prices, as significant percentages reported increased attention to vehicle maintenance (presumably to ensure peak fuel efficiency), driving slower, and driving at steadier speeds.” Work by Phil Goodwin has also found fuel consumption tends to drop further than miles driven in response to rises in the real cost of fuel, indicating alterations to driving style.

The Australian study I refer to in the piece was conducted by the Royal Automobile Club of Victoria, comparing a Ford Falcon with a Mazda Astina. If you’re still not convinced about the driving style argument, consider this note from the researchers: “A large vehicle driven conservatively can now better the fuel economy of a small car driven aggressively.”

The RACV “Fuel Smart” trial was cited within another interesting Australian study (download here), by Narelle Haworth and Mark Symmons of Monash University, titled “The Relationship Between Fuel Economy and Safety Outcomes.” Looking at a pool of fleet vehicles, they came to an interesting, though perhaps not surprising, conclusion: “The fuel consumption rate of crash-involved vehicles was higher than that of vehicles not involved in crashes.” (more…)

Posted on Sunday, June 29th, 2008 at 8:13 am by: Tom Vanderbilt
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Boy Racers

I went karting earlier this week in London, at the excellent Docklands Raceway in Greenwich, with the fine folks at Penguin and a number of intrepid, lead-footed souls from the top UK bestsellers (Waterstone’s, WH Smith, Borders, etc.). The kindly track manager told us only afterwards (thankfully), as we sipped Peronis in the bar, that in one instance a kart (they can go 45 mph) had flipped, albeit at a former facility, and the driver had to be air-lifted to the hospital.

The evening wasn’t intended as a study of driving behavior, but it was hard not to notice the gender disparity in the race results: i.e., the top finishers, in total laps, with a few exceptions, were largely male. Whether this has to do with skills per se, risk-taking, or just cultural pressure and expectation is a huge, messy issue that I won’t plunge into here. But studies bear out that males, by just about every objective external measure (speed, following distance, etc.) drive more aggressively. Perhaps some of this is hard-wired. The noted psychologist Simon Baron-Cohen, for example, has noted in his controversial book The Essential Difference, that when a group of plastic cars are left for tots to play around with, the boys tend to do things like start ramming into one another, while the girls tend to ride around more carefully — when they can actually get a car (this raises a potential topic for a study: Do societies with higher numbers of women drivers have superior traffic safety records than those more dominated by men?).

And it was certainly the men who were getting into more scrapes at the Docklands (I myself netted what was said to be the evening’s only “black flag,” for having passed another racer under a yellow flag condition; I blamed, weakly, insufficient knowledge of the rules). Whatever this evening proved or disproved about gender and driving, I was reminded of a finding by the U.K. Driving Standards Agency: Males tend to have a higher pass rate on their “practical” driving tests (the in-car portion), suggesting confidence and perhaps higher ability; but ironically, the ones who do best tend to have the highest accident rates. Driving “skill” is a mixed blessing indeed.

Posted on Friday, June 20th, 2008 at 2:17 pm by: Tom Vanderbilt
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Traffic Tom Vanderbilt

How We Drive is the companion blog to Tom Vanderbilt’s New York Times bestselling book, Traffic: Why We Drive the Way We Do (and What It Says About Us), published by Alfred A. Knopf in the U.S. and Canada, Penguin in the U.K, and in languages other than English by a number of other fine publishers worldwide.

Please send tips, news, research papers, links, photos (bad road signs, outrageous bumper stickers, spectacularly awful acts of driving or parking or anything traffic-related), or ideas for my Transport column to me at:

For publicity inquiries, please contact Kate Runde at Vintage:

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Upcoming Talks

April 9, 2008.
California Office of Traffic Safety Summit
San Francisco, CA.

May 19, 2009
University of Minnesota Center for Transportation Studies
Bloomington, MN

June 23, 2009
Driving Assessment 2009
Big Sky, Montana

June 26, 2009
PRI World Congress
Rotterdam, The Netherlands

June 27, 2009
Day of Architecture
Utrecht, The Netherlands

July 13, 2009
Association of Transportation Safety Information Professionals (ATSIP)
Phoenix, AZ.

August 12-14
Texas Department of Transportation “Save a Life Summit”
San Antonio, Texas

September 2, 2009
Governors Highway Safety Association Annual Meeting
Savannah, Georgia

September 11, 2009
Oregon Transportation Summit
Portland, Oregon

October 8
Honda R&D Americas
Raymond, Ohio

October 10-11
INFORMS Roundtable
San Diego, CA

October 21, 2009
California State University-San Bernardino, Leonard Transportation Center
San Bernardino, CA

November 5
Southern New England Planning Association Planning Conference
Uncasville, Connecticut

January 6
Texas Transportation Forum
Austin, TX

January 19
Yale University
(with Donald Shoup; details to come)

Monday, February 22
Yale University School of Architecture
Eero Saarinen Lecture

Friday, March 19
University of Delaware
Delaware Center for Transportation

April 5-7
University of Utah
Salt Lake City
McMurrin Lectureship

April 19
International Bridge, Tunnel and Turnpike Association (Organization Management Workshop)
Austin, Texas

Monday, April 26
Edmonton Traffic Safety Conference
Edmonton, Canada

Monday, June 7
Canadian Association of Road Safety Professionals
Niagara Falls, Ontario

Wednesday, July 6
Fondo de Prevención Vial
Bogotá, Colombia

Tuesday, August 31
Royal Automobile Club
Perth, Australia

Wednesday, September 1
Australasian Road Safety Conference
Canberra, Australia

Wednesday, September 22

Wisconsin Department of Transportation’s
Traffic Incident Management Enhancement Program
Statewide Conference
Wisconsin Dells, WI

Wednesday, October 20
Rutgers University
Center for Advanced Infrastructure and Transportation
Piscataway, NJ

Tuesday, March 8, 2011
Ontario Injury Prevention Resource Centre
Injury Prevention Forum

Monday, May 2
Idaho Public Driver Education Conference
Boise, Idaho

Tuesday, June 2, 2011
California Association of Cities
Costa Mesa, California

Sunday, August 21, 2011
American Association of Motor Vehicle Administrators
Milwaukee, Wisconsin

Wednesday, October 26, 2011
Attitudes: Iniciativa Social de Audi
Madrid, Spain

April 16, 2012
Institute for Sensible Transport Seminar
Gardens Theatre, QUT
Brisbane, Australia

April 17, 2012
Institute for Sensible Transport Seminar
Centennial Plaza, Sydney
Sydney, Australia

April 19, 2012
Institute for Sensible Transport Seminar
Melbourne Town Hall
Melbourne, Australia

January 30, 2013
University of Minnesota City Engineers Association Meeting
Minneapolis, MN

January 31, 2013
Metropolis and Mobile Life
School of Architecture, University of Toronto

February 22, 2013
ISL Engineering
Edmonton, Canada

March 1, 2013
Australian Road Summit
Melbourne, Australia

May 8, 2013
New York State Association of
Transportation Engineers
Rochester, NY

August 18, 2013 “Ingenuity” Conference
San Francisco, CA

September 26, 2013
TransComm 2013
(Meeting of American Association
of State Highway and Transportation
Officials’ Subcommittee on Transportation
Grand Rapids MI



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