Archive for the ‘Risk’ Category

Epidemics, Continued

I earlier ruminated on what might happen to traffic fatalities in the midst of the swine flu epidemic (and noted the vast gulf between the numbers of deaths from both causes).

An answer of sorts has come from Mexico City, from Eric Britton over at World Streets. Via the newspaper Reforma, we learn:

Apparently the swine flu in Mexico City caused few real deaths but many traffic deaths. The large drop in the volume of cars increased velocities and also increased traffic fatalities. There were 12 traffic fatalities in the 6 days before the government issued their swine flu alert and 75 traffic fatalities in the 6 days after.

Here is the kicker: the increase in traffic deaths (63) dwarfs the number of swine flu deaths (8) during those six days.

This is hardly scientific, and I’m dubious increased speeds would be the main reason — I’d guess instead higher exposure from people avoiding public transit — but it is certainly suggestive.

Posted on Thursday, May 28th, 2009 at 8:44 am by: Tom Vanderbilt
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Sticker Shock

A few winters ago, I found myself in Copenhagen’s Tivoli Gardens at Christmastime. I was struck by the presence of a number of open-air containers holding little burning piles of coal (or some such), cheerily blazing through the Danish night. What got my attention is that these were in no way marked or restricted. There were no ominous warning signs (Caution: Coals are Hot When Heated!), no barriers, no minders, no consent forms to sign. And surprisingly, there were no mass incinerations of Danes on the spot, no burning children running in terror, no medics on the spot administering salve and bandages (unless I missed that study, “On the Prevalence of Second-Degree Hand Burns at an Unprotected Heat-Emitting Device: A Weighted Exposure Analysis,” in the Royal Danish Journal of Random Minor Public Risks). Just people warming their hands, drinking their glog, and moving on.

Back in the litigious U.S., I am constantly reminded of that moment in Copenhagen. The most recent event to do this was the purchase of a rear-facing infant car seat (yes, some of you predicted there would be infant car seat posts!). Now, this is not necessarily an object one buys for aesthetic reasons, but I was dismayed to find any number of yellow-and-black warning stickers pasted all over its frame (in multiple languages), essentially warning me not to put this rear-facing infant car seat in the front seat. Given that my car doesn’t have the NHTSA-approved “latch” system in the front seat, I’m not quite sure how I’d even do this, but in any case the stickers are almost impossible to remove. Now, this is a device for which one needs to read the instruction manual rather carefully to install (of course, many people do not), so I’m not sure why it also requires a profusion of permanent warning stickers as backup. Maybe I’ll loan my car, car-seat, and infant to someone else? Well, wouldn’t I make pretty darn sure that person knew not to put the car seat in the front seat? Perhaps someone will steal my car and put my infant car seat in the front seat, smash it up, then sue me?

The reason the car seat is not supposed to go in the front seat, of course, is that it would, among other things, run the risk of being impacted by the front passenger airbag. And I know all about this device because of the virtually impossible to remove warning stickers that are plastered to the visor, warning me, in various ways, about having small, unrestrained children in the front seat! Being of sound mind and body, and having absorbed the knowledge about this via the car’s manual (among other sources), I had thought this sticker could be removed (and isn’t there something a bit creepy about a safety device coming with a warning in the first place?), but it stays to this day (apparently there are incredibly labor intensive, and not guaranteed, ways to remove it).

I am all for safety, but do we really, apart for any reason other than a potential lawsuit against a company (and I wonder how many of these been launched against the auto/car-seat makers when the product is used in an inappropriate manner), need these omnipresent warning stickers? Are we saying that we have entrusted someone enough to drive a car in the first place (a process that admittedly has been made too easy in the U.S.), have a child (er, ditto), and then still not possess sufficient intelligence to know how to handle safety devices and infants? Why must I “subsidize” — with these offensive stickers all over my stuff — the foolish acts of others? There are myriad ways to die in a car — mostly having to due with negligent acts by the driver involving the actual act of driving, as well the unlawfully high speeds these machines so easily attain (there’s no warning sticker on the speedometer, mind you) and not seating infants in the front seat. Why don’t we direct some of this attention that way?

Then we can take all these warning stickers, gather them up, and roast them in a big bonfire in Tivoli Gardens — just make sure to sign the release form.

Posted on Friday, May 15th, 2009 at 2:29 pm by: Tom Vanderbilt
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‘The More You Protect a Crossing, the Worse People Behave’

I’ve been interested in the work of UC-Berkeley’s Douglas Cooper and David Ragland on crashes at railway crossings. Looking at incidents that occurred between 2000 and 2004 in the state of California, they found that “of the crashes that occurred, 73 percent occurred at crossings equipped with gates, 59 percent involved vehicles moving over the crossing, and 27 percent involved vehicles that had driven around or through lowered gates. An unbelievable number, 21 percent, involved a vehicle running into a moving train.”

I couldn’t help but think of those findings when I recently came across the following remarkable passage in John Stilgoe’s book Metropolitan Corridor: Railroads and the American Scene, describing the early problem of dealing with vehicular traffic at railroad crossings:

“Adding gates, bells, and electric flashing lights at some crossings at first seemed to help, especially if the gates overlapped each other to prevent motorists from snaking past them onto the tracks. But by 1913, experts knew that numerically as well as comparatively more persons are killed at protected crossings,” at crossings defended by watchmen, gates, bells, lights, and signs. What accounted for “comparatively”? Certainly protected crossings usually passed many more wayfarers than unprotected rural crossings far from towns, but why did proportionately more people collide with trains there? Did carelessness born of some mad scurrying haste account for the deaths, or was it the old “familiarity with the timetable” syndrome? If anything, a sort of early-twentieth-century highway hypnosis might explain the accidents at protected crossings. “How many of you readers heard your clock strike at the most recent hour?” asks Whiting in his 1913 article. People intimately familiar with their route to work, to shopping, to school, simply did not realize the protected crossings. Lost in some sort of waking trance, they walked past the lights or drove directly into and through the gates. “Disgusted railroad men will sometimes tell you that the more you protect a crossing, the worse people behave,” Furnas noted in 1937. “They seem to figure that if the company has taken all that trouble, the drive is absolved of responsibility for himself.” So concerned were California authorities that as early as 1917 they began designing speed bumps into paved highways approaching crossings, hoping that a violent jarring would knock motorists out of their trances and apprise them that they “should cut down speed and be on the lookout for warning signals.” By 1937, after the speed bumps had increased in height to two or three feet, one magazine writer concluded that they did nothing to alert motorists. Drivers simply breezed over them, crashed through gates, and struck trains. When reformers suggested that railroad companies install gates so solid that motorists could not break through them, companies replied that such gates could not be designed. The flimsy gates, they explained, existed to permit motorists to crash through both pairs and escape death, or through the far pair if they entered the crossing as the gates lowered. By the early 1930s, the protected grade crossing displayed the gadgets of mechanical, electrical, and efficiency engineers—and all of the engineers had failed.”

An interesting early example of the challenges of safety engineering in light of human risk compensation, and clearly a longstanding problem that has not been solved.

Posted on Thursday, May 14th, 2009 at 11:30 am by: Tom Vanderbilt
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Yet another driver is implicated in texting while driving — this time a trolley in Boston. Given the trouble that highly trained drivers have with distracting technologies, it doesn’t require much imagination to think what’s happening to the average car driver as they remotely engage.

Posted on Monday, May 11th, 2009 at 8:36 am by: Tom Vanderbilt
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The Invisible Hand

David Williams of the Telegraph gives a prototype vehicle equipped with Intelligent Speed Adaptation (what used to be known as a “governor”) a spin through London. The car limits speed to whatever the limit is on the segment — typically 30 mph.

This line struck me:

Like most motorists I want to be law-abiding. Up until now I’d believed I was. But this clever car exposes such self-delusions. Normally I try to keep to 30mph in town but in reality I must have been doing nearer 40 as I never drive this slowly.

Someone recently asked me, “why do people speed?” There’s no short answer to that question (I’ve got 250-page reports tackling the question), but one possibility that must be considered, in light of the above sentences, is that: They actually don’t know how fast they are going. Any number of studies have shown how drivers, particularly when the feedback is noisy — i.e., they’re sitting high up from the road, the car cabin is ultra quiet (or the radio loud), the road is very wide — routinely underestimate their speed.

As we’ve banged on here about many times before, these minor differences in urban speed, while inconsequential and almost imperceptible for the driver, can be of dramatic importance for the pedestrian or cyclist struck by a vehicle.

Posted on Monday, May 11th, 2009 at 8:30 am by: Tom Vanderbilt
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Bad News for Traffic Signal Manufacturers

From the Times of London, a story that seems “ripped from the pages” of Traffic.

The always good transpo correspondent Ben Webster asks:

What would happen if traffic lights were suddenly switched off? Would there be gridlock or would the queues of frustrated drivers miraculously disappear?

People in London are about to find out the answer in Britain’s first test of the theory that removing lights will cure congestion.

For six months, lights at up to seven junctions in Ealing will be concealed by bags and drivers will be left to negotiate their way across by establishing eye contact with pedestrians and other motorists.

The reason for the trial was pure accident:

Ealing found evidence to support its theory when the lights failed one day at a busy junction and traffic flowed better than before. Councillors have approved a report which recommended that they “experimentally remove signals since experience of signal failure showed that junction worked well.”

Of course, careful attention will have to paid to safety results, particularly with pedestrians (the piece refers to some new mid-block crossings but one has to entertain the idea that these treatments may reduce pedestrian’s perception of safety and thus, potentially, one’s inclination to walk). The one day of outage could have represented a novelty effect. But the interesting thing about these novel treatments is that they are often done with much more care and concern than the standard “out of the book” approach that is applied automatically.

Ealing Council believes that, far from improving the flow of traffic, lights cause delays and may even increase road danger. Drivers race towards green lights to make it across before they turn red. Confidence that they have right of way lulls them into a false sense of security, meaning that they fail to anticipate hazards coming from the side. The council hopes that drivers will learn to co-operate, crossing junctions on a first-come first-served basis rather than obeying robotic signals that have no sense of where people are waiting.

(Horn honk to Prashanth)

Posted on Saturday, May 2nd, 2009 at 3:22 pm by: Tom Vanderbilt
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Bike Locally

I found the most telling — and really, the only actionable — bit of this whole piece in the New Scientist piece about a computer model on the pros/cons of mandatory cycle helmet laws came in the last line:

However de Jong, a native of bike-loving Holland, makes clear that he would not discourage people from wearing helmets. “I go to Holland and places like that, and I don’t wear a helmet,” he says. “I used to live in London, and I wore a helmet all the time.”

Posted on Monday, April 27th, 2009 at 11:14 am by: Tom Vanderbilt
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Bustle in Your Hedgerows

A great anecdote from an article in Smithsonian (which quotes Traffic) on risk compensation:

Soon after the first gasoline-powered horseless carriages appeared on English roadways, the secretary of the national Motor Union of Great Britain and Ireland suggested that all those who owned property along the kingdom’s roadways trim their hedges to make it easier for drivers to see. In response, a retired army colonel named Willoughby Verner fired off a letter to the editor of the Times of London, which printed it on July 13, 1908.

“Before any of your readers may be induced to cut their hedges as suggested by the secretary of the Motor Union they may like to know my experience of having done so,” Verner wrote. “Four years ago I cut down the hedges and shrubs to a height of 4ft for 30 yards back from the dangerous crossing in this hamlet. The results were twofold: the following summer my garden was smothered with dust caused by fast-driven cars, and the average pace of the passing cars was considerably increased. This was bad enough, but when the culprits secured by the police pleaded that ‘it was perfectly safe to go fast’ because ‘they could see well at the corner,’ I realised that I had made a mistake.” He added that he had since let his hedges and shrubs grow back.

I couldn’t help also think of a story today about a woman killed by a reckless driver (police think he was racing, and manslaughter charges are a possibility) in San Diego.

“Route 67 between Poway Road and Ramona has been the scene of numerous fatal crashes over the years. Calls to widen the winding route have been made for some time, but transportation and highway patrol officials say the real problem isn’t with the road but with the way people drive on it… Speeding is responsible for most of the crashes, they say.”

It’s amazing how short-sighted (not seeing the forest for the, er, hedgerows) people can be in this respect; widening the road is absolutely the last thing that will reduce what seems to be a speed problem.

Posted on Wednesday, April 1st, 2009 at 11:49 am by: Tom Vanderbilt
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Killer App

The long-elusive silver bullet of traffic safety, if you read this press release, has arrived in the form of the … iPhone!

From the same company that produces a “speed trap” detection application for the iPhone, thus decreasing the safety of the road both in terms of speed and distraction, comes this bold claim: ( added another layer to their Speed Trap mapping system today by including traffic accidents and fatalities to enhance their data visualization system. This addition will allow drivers to see where accident black spots and problem areas are. An updated Njection Mobile iPhone application [iTunes] ( that allows drivers to be alerted to these high accident areas is awaiting approval from Apple.

[uh, quick interjection; a good deal of crash blackspots are at intersections, which are typically controlled by traffic lights, and sometimes, because people don’t seem capable of obeying simple traffic signals, red light cameras, which your software will also sniff out — thus potentially increasing the very crash blackspot-ness! How wonderfully intregrated!] has acquired accident data from the National Highway Traffic Safety Administration (NHTSA – and global weather conditions from (, and coupled this information with Microsoft Virtual Earth ( to produce a unique use of data visualization. This Virtual Earth mash-up not only allows users to view 5 years of accident data collected from the NHTSA based on local weather conditions but to see it in 4-hour blocks updated every hour from the current time. For example, if it is 12PM and a user selects the “4 hour history” radio button, they will be shown a history of accidents that have occurred between 11AM and 3PM based on the local weather conditions.

I realize this is a press release (regurgitated without comment by Fox Business), and not to mention this is still early days for the iPhone — every app is announced with breathtaking excitement, but most will be revealed as useless geegaws, to be marveled at over drinks for fifteen minutes with your friends and then cast into the silicon attic.

But apart from the incredible irony of this company suddenly being concerned with “safety” this is incredibly wrong-headed on several fronts. First, as any number of SatNav crashes have shown, taking drivers eyes and minds off the road, reducing their situational awareness, is not a good idea. Full stop. Rather than scanning some tiny screen to look for time-and-weather coded crash data, one should actually be looking at the actual conditions of the road one is on.

Then, there’s the problem of regression to the mean. A place may be an “accident black spot” for a time, then have no crashes for the next number of years. What are we to do with that information? And, given that the vast majority crashes have driver behavior at their root, not slippery bridge surfaces and the like, presenting crash data as somehow a function of road conditions is disingenuous. And, as always, does highlighting places of greater crash frequency leave one less vigilant at other locations?

The best way the iPhone could contribute to traffic safety in the car — apart from the long-awaited breathalyzer app — is it for it to be turned off.

Posted on Wednesday, April 1st, 2009 at 8:28 am by: Tom Vanderbilt
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The Future Eventually Arrives

Traffic gets up a great write-up over at Popular Mechanics, via Glenn “Instapundit” Reynolds. Here’s an excerpt:

The safety-through-danger approach extends to cars. Modern cars are quiet, powerful and capable of astonishing grip in curves, even on wet pavement. That’s swell, of course, until you suddenly lose traction at 75 mph. The sense of confidence bred by all this capability makes us feel safe, which causes us to drive faster than we probably should. We don’t want to make cars with poor response, but perhaps we could design cues—steering-wheel vibration devices, as in video games?—that make us feel less safe at speed and encourage more care. Designers could make cars feel faster at lower speeds, instead of slower at higher speeds. Done right, this might even make driving more fun. In college I drove an Austin-Healey 3000 that somehow felt faster at 45 mph than my Mazda RX-8 (or even my Toyota Highlander Hybrid) feels at 75 mph. That was a good thing.

This approach could be taken beyond the world of personal transportation. We’re in the current financial mess in part because things that were actually dangerous—from subprime mortgages to risky financial instruments that no one fully understood—felt safe and ordinary. Modern financial markets, with computers, regulations, deposit insurance and bond ratings, felt as routine and as smooth as that four-lane highway in Spain, causing a lot of people who should have been paying attention to doze off. Investors might have been more careful if it had felt like they were driving down a twisty mountain road with no guardrails, especially since we really were engaged in the financial equivalent of high-speed mountain driving, only without the discipline of fear.

In athletics, protection sometimes leads to more risk-taking. Research has shown that skiers who wear helmets ski faster than those who do not. Likewise, firearms instructors are quick to stress that the safety on a gun doesn’t actually render the weapon safe, just marginally safer, so that all usual precautions still apply. And I noticed when scuba diving with a spare air cylinder that instructors were concerned these backups would become popular with inexperienced divers and that this reliance might breed carelessness with the main equipment.

The traffic example demonstrates a general phenomenon of modern society: With the best of intentions, we tend to replace situations that call on the use of our wits with situations that we can sleepwalk through, and the solutions to matters with any serious consequences are postponed to the indefinite future. That’s a comfortable way to live, and there are good reasons to be glad of it—we’re not in a situation where one bad harvest means starvation, after all—but if you can postpone problems indefinitely, a lot of problems will be postponed. Yet the future eventually arrives.

Posted on Tuesday, March 31st, 2009 at 6:46 am by: Tom Vanderbilt
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More on the Geography of Danger

This map, of bicycle crashes in Toronto, was mentioned in the comments to the original post. And then there’s Transportation Alternatives’ invaluable crash maps. Projects like this loom on the horizon. I’d be curious to know what others are out there.

The potential impact GIS (and real-time mapping) has for traffic safety (among other things) seems great, particularly as we can add sophistication to the layers: Time of day, exposure data, road characteristics, etc. Some of this requires hard coding, but I’m wondering what other information could be gleaned from mobile phones and the like. The obvious source of interest would be something like pedestrian volumes and walking speeds, as recorded by iPhones and the like; too many pedestrians moving too slowly up Fifth Avenue — extend the walk signal! But other uses can be imagined as well; “dwell time,” the amount of time pedestrians spend in public areas, could be measured, for example. Or how quickly pedestrians cross streets (this could be part of a larger Christian Nold-style “bio-mapping project” to measure particularly unpleasant intersections and the like). Vibration-sensitive PDAs could monitor potholes on streets and in bike lanes. Sensors could detect “honks” and a “honk map” could be created, with targeted police enforcement and selective traffic engineering solutions. Credit cards could be synced up with MetroCards or EZPasses to determine how much economic activity in the city each form of transportation brings. Data on red-light running from camera-equipped intersections could be fed anonymously to in-car GPS systems, as well as those on the personal devices of pedestrians. The possibilities are legion.

One of the myriad problems with mapping risk is that the numbers, particularly when exposure data is absent, can lack explanatory power. Oh, there were no pedestrians struck this year on the F.D.R. Drive — this obviously does not imply a street that is safe for pedestrians. And while I do feel, like Pascal, that most of man’s unhappiness comes from not being able to simply stay quietly in his room, one must leave the house, and overhyping everyday dangers can be its own form of danger.

An interesting phenomenon in terms of risk and the built environment is that what we perceive as risky is not always the place where the risk actually lies (and it’s an interesting question as to whether this misperception itself leads to the risk profile). An interesting study at the University of North Carolina looked at students’ perceptions of pedestrian risk on campus versus perception and found that the two did not always correlate. The study found all sorts of curious detail, as charted in the image below (which shows a relatively equal distribution of crashes but certainly not an equal distribution of risk perception); e.g., there were more crashes near places like the stadium than people believed there were (there are certain biases to be careful of; proximity to a building in general increases the reporting of crashes, which may throw off the actual risk profile).

Posted on Monday, March 23rd, 2009 at 5:50 pm by: Tom Vanderbilt
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The Geography of Danger

A map via This is London (thanks Berkeley TSC) that pinpoints bicycle crashes in 2007. While an interesting first step, it doesn’t link up to details on exposure details, nor street characteristics, nor time of day, nor exact crash causality — not to mention the danger itself that people view a couple of red dots on their street and think they see a pattern when regression to the mean may see no incidents on that street for the next few years.

But this hints at the evolving potential of GIS, etc.

Posted on Friday, March 20th, 2009 at 2:30 pm by: Tom Vanderbilt
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Lane Splitting

The earlier posting on late merging reminds reader Joel of the issue of “lane splitting,” by which motorcyclists (and sometimes bicyclists) ride in the space between cars, ideally in heavy traffic. This is legal in California and other states, but, as he points out, it seems to raise drivers’ hackles (in places like Rome, of course, it’s an everyday fact of life, as scooters by the dozens “filter” between cars to settle near the front of stopped queues at traffic lights).

It’s an interesting, much-discussed issue (see here or here for example) because it raises so many of the issues that come up in traffic: Social justice (hey, why are they allowed to move when I’m stuck in traffic), different modes sharing the same road space, trading off risks, not to mention cognitive psychology.

Like so many things in traffic, it’s complex. In theory, I like the idea — why shouldn’t we use as much road space as possible? (the extra lane space put in for safety at high speeds is essentially wasted during congestion). A motorcycle between streams of cars shortens the length of the queue for cars, after all (and unlike HOV or hybrid lanes, doesn’t reduce existing highway space). On the other hand, there have been times when I’ve been absolutely startled by a motorcyclist unexpectedly passing me. This raises the question of the “attentional set”: If we don’t usually expect motorcycles to be there, will we not see them as we change lanes, or if we unintentionally “drift” a bit? (for the biker, the added problem is the people who don’t signal before changing).

And yet the smaller visual profile of motorcycles means we may not see them in front of us as easily as a car — not to mention the fact that the small fender-bender of stop-and-go traffic means more to a cyclist’s health than a car driver’s — and this brings up the point that has always been made vis a vis lane splitting: That being rear-ended by a car is a much greater hazard than riding between the lanes. The leading authority on this, and motorcycle safety in general, is Harry Hurt, author of the famous “Hurt Report” and now based here, who is quoted here as saying: “For a motorcyclist, that’s the safest place to be [between streams of traffic]… A lot of people think it’s a hazard, but the cold, hard facts are that it’s not.”

As far as I know, the “Hurt Report” has never been duplicated in size or scope, even as more motorcyclists have hit the road. The author himself seemed to think its 1970s-era findings, however, still hold valid.

As it happens, yesterday I was just reading a piece in Outside about the idea of bringing Asian-style “motorcycle taxis” to the U.S. The piece notes:

In the U.S., moto-taxis face two main obstacles. The first is insurance. When EagleRider, now the largest motorcycle-rental company, initially shopped for insurance, their rates were three times what they’re paying now. The second problem is a traffic law in 37 states that bans “splitting”—the practice of riding between lanes. Sounds unsafe, but even when allowed, it accounts for only 3 percent of motorcycle fatalities. When it’s outlawed, you’re stuck in crosstown traffic just like everyone else, only you’re breathing exhaust.

The 3% number is interesting; then again, if lane-splitting was only done when it is supposed to be, during slow or stopped heavy traffic, I wouldn’t expect large numbers of fatalities.

Any motorcyclists out there care to weigh in? Cyclists? Drivers? People selling things at traffic lights? (they too lane split)

And just to muddy the waters, speaking of social justice and road sharing, I’ve been annoyed lately to see motorized scooters chugging along in the bike lanes in Brooklyn and elsewhere. My knee-jerk reaction is ‘that’s not what their for” and ‘I don’t want your exhaust in my face’; but maybe I’m too harsh — perhaps if it’s otherwise unoccupied it’d be OK. But while it may make them feel safer, they may only be raising their exposure to “dooring” and other hazards.

Posted on Wednesday, February 25th, 2009 at 12:31 pm by: Tom Vanderbilt
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“The Life You Might Save Might Be Mine”

James Dean’s eerily prophetic traffic safety PSA, filmed on the set of Giant. Some later work has tried to sort out why the crash happened (arguing for the inconspicuity of Dean’s car and perhaps a form of “inattentional blindness”).

An article in the Telegraph goes on to assert:

“Now, new evidence has emerged proving that not only was Dean driving safely, but at a much lower speed than was believed at the time.

It has long been part of Hollywood lore that Dean, with his passion for fast cars and reputation for rebellious behaviour, was driving his high-powered Porsche Spyder 550 when he and Rolf Weutherich, a mechanic, smashed into another car on a Californian highway.

A ground-breaking documentary by Channel 5, however, has unearthed evidence that Dean, contrary to what was said at the inquest into his death, was travelling at just over 70mph, up to 20mph slower than was claimed. It reveals that Dean braked hard, trying to avoid the car that cut across him, rather than using the throttle to accelerate around it, as was alleged at the time.”

Just over 70 mph on a state highway represents driving “safely”? (Dean had already received one speeding ticket before the crash; not to mention the crash protection of that era’s cars was minimal). This is not a scientific term. Would a 55 mph Dean have survived?

Posted on Saturday, February 21st, 2009 at 6:15 pm by: Tom Vanderbilt
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What’s the Real Risk of Older Drivers?

Nothing brought the issue of older drivers into sharper focus than the 2003 crash at the Santa Monica Farmer’s Market, in which a 86-year-old man who had confused accelerator for brake killed nine people and injured scores more. As often happens in the media, something that had once basked outside of the light of attention suddenly became an “epidemic,” and untold numbers of stories warned us of the specter of the aging Baby Boom behind the wheel. This is, undoubtedly, a real issue, and the problems of the older driver do merit societal attention, but it is also likely that the circumstances of the Santa Monica event may have helped skew the actual risk posed: It was novel, it represented something out of our control, and, compared to most traffic fatalities at least, a large number of people were involved.

A new paper by Bryan Tefft, a researcher at the AAA Safety Foundation, published in the latest edition of the Journal for Safety Research, tries to put the older driver risk question into context, addressing some shortcomings of previous studies, most of which have not, as he notes, “analyzed responsibility for — as opposed to mere involvement in—crashes that kill other road users in relation to driver age, and none has done so while taking the amount of driving done by drivers of different ages into account.”

It is a truism of road safety research that a kind of u-shaped curve exists, in which the riskiest drivers are found at both ends of the age spectrum, as shown in the chart below, which comes from a Rand study (more on that later).

But this leaves out various, but important, parts of the risk equation, including: Which drivers (if any) bore a greater responsibility for the crash (an admittedly “noisy” bit of data), and the risk posed by certain classes of drivers to other drivers.

In any case, Tefft, using data from the FARS database, as well as “exposure” data from the National Household Travel Survey (and he notes using two different sources is a limitation of the work), comes to some interesting conclusions.

As other studies have found, he notes older drivers do have a greater risk of being involved in a fatal crash, but that this fatality risk is largely to themselves, as they are more likely, owing to increased “fragility,” to die in a crash than a younger driver. But as Tefft notes, “the degree to which older drivers’ risk to other road users is elevated depends strongly upon whether risk is measured on a per-driver, per trip, or per-mile basis.”

As an example, he writes, “if a randomly-selected driver in his or her thirties and a randomly selected driver aged 85 or older were to drive equal numbers of miles, the older driver would be over 1500% more likely than the younger driver to be responsible for and die as a result of a crash, and about 220% more likely than the younger driver to be responsible for a crash fatal to an occupant of another vehicle or a non-motorist.”

But, of course, most older drivers don’t drive as much as younger drivers, and they drive differently (i.e., they modulate risk based on their ability by choosing only certain roads, or certain times of day to drive, they may drive more slowly — insert Florida joke here — etc.). And so, while “a randomly-selected driver aged 85 or older is about 720% more likely than a randomly selected driver aged 30 to 39 to die in a crash, but only about 0.8% more likely to be responsible for a crash fatal to an occupant of another vehicle or a non-motorist, over the course of a year.” Per trip, the risk older drivers pose to others is “not statistically different” from drivers 30 to 39.

For the greatest source of risk from “without,” then, we need to look at the other end of the age spectrum. Tefft writes: “Drivers under age of 20 are responsible for more than twice as many deaths of occupants of other vehicles and non-motorists as are all drivers aged 70 and older.”

Tefft’s findings are supported by another paper — which uses another methodology (based on a technique created by Steven Levitt and J. Porter in this paper, which uses the drivers involved in fatal crashes as a surrogate for exposure) — namely, the Rand study mentioned above, “Regulating Older Drivers: Are New Policies Needed?,” by David S. Loughran, Seth A. Seabury, Laura Zakaras. They conclude: “In summary, we find that older drivers are only slightly likelier than other drivers to cause an accident but are considerably likelier to be killed in one. Younger drivers, on the other hand, are considerably likelier than other drivers to cause a crash, drive much more frequently than older drivers, and are less susceptible to fatal injuries than older drivers are.”

There are good reasons to be concerned about older drivers, but the news stories suggesting the greatest threat to our safety might come at the wrinkled hands of aging drivers seems somewhat misplaced. In strict terms of cost and benefit, it would seem wiser (assuming older drivers continue to do less driving than their younger peers), rather than rolling out new “mandatory retesting” programs in state DMVs (granted, one must leave open the possibilities these already existing programs have impacted the older driver crash rate), to ratchet up GDL programs at the other end — it really is shocking that driver’s licenses, in states like North Dakota, can still be had at age 14. Or simply cracking down on the most risky drivers, regardless of age, rather than blithely allowing people with clear patterns of dangerous driving to inhabit the roads (and, by the way, please don’t start on the sob story, ‘but it’s the U.S., you can’t function without a car…’). Demonizing older drivers may also subtly suggest to younger drivers, in their 30s say, that they have much less to worry about, when as Teftt’s per trip numbers indicate, may not be the case.

Posted on Friday, February 20th, 2009 at 12:31 pm by: Tom Vanderbilt
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Bad Cycling? Bad Science

Here is what insurance company LV has to say about cycling safety in the U.K.:

“Mounting financial pressures have led to a surge in inexperienced cyclists taking to the roads,” say LV in their press release: “resulting in a 29% increase in road accidents involving cyclists in the past six months.”

This from a press release titled: “ROAD USERS WARNED OVER INEXPERIENCED CYCLISTS.” Road users aren’t the same as cyclists, inexperienced or not?

And here’s what Bad Science author Ben Goldacre says: “It’s topical, it involves death and fear, it’s dressed in the cloak of statistical authority: this is totally going on the telly.”

Read his full dissection here. The problems seem legion; for beginners, we don’t know that the cyclists hit are indeed the novel cyclists. These sorts of insurance-company led “studies” come up all the time in the media, and I’m not sure whether they’re done as PR stunts (I love that phrase “PR-reviewed scientific evidence”) for a willing media, or to scare us all into buying more insurance (or maybe getting us off the bike and into a car). There are real issues here, but head-line chasing does no one a service.

Posted on Wednesday, February 18th, 2009 at 3:18 pm by: Tom Vanderbilt
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Dangerous Roads, or Dangerous Driving?

This piece from Fox News (after the jump as well) claims to identify the “top 10 most dangerous roads in America,” implying as well that stimulus spending might somehow be directed to these corridors of death.

But reading through the piece, the overwhelming impression left with me is not design or infrastructural shortcomings, but driver shortcomings: Speed, alcohol, fatigue.


Posted on Thursday, February 12th, 2009 at 8:15 am by: Tom Vanderbilt
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Unsafe Routes to School

There is a strange sort of consensus in this tragic tale from Atlanta of a child killed as he was crossing in front of his school that somehow, lack of traffic signals is the underlying problem.

Traffic signals, however, despite our fetishistic belief in them, are not a safety device per se: They are a means for directing traffic flow. To the extent they actually get drivers to stop (for fear of being struck by another car), they have an ancillary benefit for pedestrians. But they also encourage drivers to look up away from the street, and to accelerate towards an intersection (potentially crowded with pedestrians) so as to not miss a light. They may also raise a false sense of security amongst pedestrians.

But as the story notes, there was no shortage of warning here:

A crossing guard was on duty and had carried a stop sign into the street, and other vehicles had stopped, police spokeswoman Mekka Parish said.

What’s more,

Road signs warn drivers they are approaching the school crosswalk. Ogilvie’s car was southbound. Drivers coming from the north pass a flashing school zone sign on a roadside post and a sign warning, “Stop for pedestrians in crosswalk” before traveling over a small hill just north of the school.

Exactly how many more warnings this driver needed (no word if they were on a phone or similarly distracted) before realizing they were in an area with crossing schoolchildren is unknown — and why, having missed all these other signs, this driver would magically stop for a traffic light (more than 3000 people a year are killed by people who don’t), is beyond me. At what point do we treat the issue of driver responsibility, instead of cursing the absence of a set of colored lights in the sky or some bit of road engineering?

The piece skirts around the real issue: Driver speeds (from experience people in the Atlanta region treat small neighborhood streets as high-speed shortcuts). It could have also noted the much greater likelihood of a pedestrian dying when struck by an SUV, rather than a car.

Posted on Wednesday, February 4th, 2009 at 5:27 pm by: Tom Vanderbilt
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Not-in-Traffic Risk

There’s an old saw that says the only safe car is the one that never leaves the driveway, but a recent report from NHTSA highlights the danger that cars can pose even before they get into traffic.

The NiTS 2007 system provided information about an estimated 1,159 fatalities and 98,000 injuries that occurred in nontraffic crashes such as single-vehicle crashes on private roads, collisions with pedestrians on driveways, and two-vehicle crashes in parking facilities.”

All the sobering details are here.

Posted on Tuesday, February 3rd, 2009 at 5:09 pm by: Tom Vanderbilt
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Model Behavior

Over a lunch I recently attended at the Applied Physics Laboratory at Johns Hopkins, the talk turned briefly to the difficulty of modeling human behavior in large-scale evacuations of people in cars, as occurred during some of the recent hurricanes. “What happens when the driver turns around and sees a big black cloud in the sky?” as one person put it.

Of course, modeling routine traffic behavior presents myriad challenges of its own, which is probably why it is still such a robust activity. As Dirk Helbing notes in his article, “Traffic and related self-driving many-particle systems,” in Reviews of Modern Physics, “Altogether, researchers from engineering, mathematics, operations research, and physics have probably suggested more than 100 different traffic models, which cannot all be covered by this review.” (the article, by the way, is 75 pages long).

Some of these consider traffic flow as a kind of fluid behavior, some have looked at the behavior of “car following,” how one driver is “attracted” and “repulsed” by the person in front of them (which then laid the challenge of how to model a single driver, with no one ahead of him), others have delved into “cellular automata.” Some have tried to break driver behavior down into a complex range of attributes. But as Philip Ball notes in his excellent book Critical Mass, “the more complex the model, the harder it becomes to know what outcomes are in any sense ‘fundamental’ aspects of traffic flow, and which follow from the details of the rules.”

So while large-scale models can with some success predict, say, the formation of traffic jams, there’s an inherent amount of built-in “noise,” e.g., human behavior. For example, I have a bit of an aversion to driving right next to someone. If I’m cruising along at a comfortable speed, but then notice a car in the neighboring lane is unnervingly keeping the same speed, I will accelerate or decelerate, to have my own pocket of space. Are all drivers like this? If not, how many? How do you model something like that? (more…)

Posted on Friday, January 30th, 2009 at 2:10 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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