Archive for the ‘Traffic Wonkery’ Category


Another item of interest I had come across in Joe Moran’s book was the “Conemaster,” an automated device for laying down traffic cones on the highway. That’s a U.K. product, but there are others, as the video — of a “single operator lane closure system” — above shows. Given the hazards posed by drivers to people working on highways, this is a clearly useful device. A bit of background:

Currently, traffic cones are deployed by a person riding on the exterior of a modified vehicle. This person is typically either standing in a basket at the end of a truck or sitting near ground level between the axles of the customized cone body truck. On the current Caltrans cone truck, two horizontal stacks of cones are fed by conveyor to a worker who then places or retrieves the cones while another person drives the vehicle.

In 1990, The State of California paid out $36,000 in injury claims related to manual cone laying. This increased over 10 time in four years to $321,000 in 1994. Available statistics suggest that this trend of increasing costs is continuing.

The AHMCT Center has developed a machine that can automatically place and retrieve traffic cones. This machine fits onto existing Caltrans traffic cone trucks and all operations are controlled from within the cab by either the driver or a second operator.

A typical lane configuration uses 80 traffic cones for each 1.5 miles of lane closure. Traffic cones come in various sizes up to 36 inches high. Caltrans uses a 28 inch high cone that weighs 10 pounds. When cones are being carried to and from stacks on the bed of a truck, personnel are restricted from carrying more than 3 cones at one time and this operation of manually transferring the cones is often performed on the roadway.

Now, where have our robotic bollards gone?

Oh, and by the way, it cleans up after itself too.

Posted on Monday, June 29th, 2009 at 1:30 pm by: Tom Vanderbilt
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Pulp Friction

I’ve been reading, with equal parts pleasure and profit, Joe Moran’s On Roads. It’s expansive, unexpected cultural history and in some ways an ideal companion volume to Traffic; while there are certain convergences, it also covers many things I would have liked to had I more space, including the 1950s conversations on designing aesthetically pleasing motorways, evolving cultural feelings towards highways themselves, among many other things. It’s U.K. oriented, so if the words Ballard, Banham, and Belisha Beacons do not present the frisson of excitement in you that they do I, be warned. It’s loaded with strange and delightful details — things like Bob Geldof working on the M25, or the so-dubbed “Mancunian Way” getting the Concrete Society award in 1968 for “outstanding merit in the use of concrete” (I’d like to thank my agent…) And, by the way, is that the very same Concrete Society that, for a brief time in the 1960s, employed the great Trinidadian writer V.S. Naipaul, a detail I got hung up on in Patrick French’s recent biography? Was Naipaul, as he banged out A House for Mr. Biswas, spending his days writing paeans to motorways?

I’ve got many pages folded over, but there is one page of particular interest for those who write about the road. As Moran notes:

Every year, more than 120,000 new books are published in Britain, creating millions of volumes that will never be opened, let alone read. Many of these unread books are shredded into tiny fibre pellets called bitumen modifier, which can be used to make roads, holding the blacktop in place and doubling as a sound absorber. A mile of motorway consumes about 50,000 books. The M6 Toll Road [as pictured above] used up two-and-a-half million old Mills and Boon novels, romantic dreams crushed daily juggernauts.

Every author lives in vague, free-floating terror of unsold pallets of his books next in line for the pulping process (after dropping through all the other Dantean levels into remainder purgatorio) but after reading the above, I can note, with distinct enthusiasm, the perverse idea that unsold copies of Traffic may some day not be read, but indeed driven upon. It could give speed reading a whole new meaning.

Posted on Saturday, June 27th, 2009 at 2:15 pm by: Tom Vanderbilt
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Commute Was Not a Noun Until 1960

David Levinson ruminates on the origins of the word “commute.” Like the word “traffic,” it seems to have had a strictly commercial orientation (to commute money at a currency exchange) originally, but then expanded to include the flow of people, not just goods.

I hadn’t seen this bit of E.B. White verse:

One who spends his life

In riding to and from his wife;

A man who shaves and takes a train,

And then rides back to shave again.

Posted on Thursday, June 4th, 2009 at 7:53 am by: Tom Vanderbilt
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From Insects to Interstates

If time permits I’ll be attending this entry at this year’s New York Science Festival (I’ve interviewed all three of the participants).

From Insects to Interstates

Friday, June 12, 2009, 7:00 PM – 8:30 PM,
Kimmel Center, NYU

Can marching ants, schooling fish, and herding wildebeests teach us something about the morning commute? In a unique melding of mathematics, physics, and behavioral science, this program examines the creative and sometimes counterintuitive solutions to one of the modern world’s most annoying problems.

Iain Couzin

Iain Couzin is Assistant Professor in the Department of Ecology and Evolutionary Biology at Princeton University. He studies the actions and interactions that give rise to collective behavior — from marching ants and swarming locusts to flocking birds and crowds of people — and what we might learn from successful swarming.

Mitchell Joachim

Mitchell Joachim is on the faculty at Columbia University and Parsons School of Design. He is a partner in Terrefuge, a New York-based organization for philanthropic architecture and ecological design. His design of a compact, stackable “city car,” developed with the MIT Smart Cities Group, won the 2007 Time Magazine “Best Invention of the Year.”

Anna Nagurney

Anna Nagurney is the John F. Smith Memorial Professor in the Department of Finance and Operations Management at the University of Massachusetts, Amherst. Her research focuses on congested transportation networks and their relationship within different systems ranging from the Internet to global supply chains to electric power generation and distribution networks.

Posted on Tuesday, June 2nd, 2009 at 5:29 pm by: Tom Vanderbilt
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The Geekiest Sentence I Read Today

“While in 1983 a pothole would need to be over 3 inches in depth and over 30 inches in
length to pose a rim damage threat to even a mini-compact vehicle, in 2006 holes as shallow as
1½ inches no more than 16 inches long could, in theory, cause rim damage.”

That’s from Influence of Road Surface Discontinuities on Safety: State of the Art Report, a new TRB circular.

The reason is “plus-size tire rims,” a form of road social signaling that basically says, “I’ve got money to spare on rims” that will soon need to be replaced.

“The principal disadvantages [of plus-size rims] are many and include cost, weight, fuel economy, ride quality and wet grip/snow traction, as well as indicate hydroplaning resistance. Perhaps more serious downsides include reduced load-carrying capacity at extremely low aspect ratio, a shift in the handling balance toward oversteer and a slight increase in rollover propensity. A further disadvantage is that the increased vertical stiffness of low aspect ratio tires means they act as shock transmitters rather than shock absorbers. Safety implications arise when a motorist will agree to replace a bent wheel that is no longer able to hold air, but will continue to use an injured tire since the damage is internal and not visible to the naked eye.” (Walter, J. Style Over Substance. Tire Technology International, March 2006.)

The authors also conclude, by the way, that potholes have little negative effect on road safety.

And one last thing: The vehicle brand above is now the property of an obscure Chinese company. Will they still be adorned with all those ultra-patriotic bumper stickers?

Posted on Tuesday, June 2nd, 2009 at 4:53 pm by: Tom Vanderbilt
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The Price of Anarchy

The network optimality problem known as Braess’ Paradox (often confused with the simpler notion of “induced demand”) can be tricky to explain, much less understand (and, like Bigfoot or the Yeti, everyone’s heard of it but we’re not sure anyone’s actually seen it in action, at least purely), but there’s a nice explanation (with illustrations) over at Gravity and Levity.

In his good, though quite technical book Selfish Routing and the Price of Anarchy, Tim Roughgarden also uses a quite entertaining example of a spring and a weight to explain the theory.

Posted on Friday, May 29th, 2009 at 7:51 am by: Tom Vanderbilt
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Some Ring Roads Are Bigger Than Others…

Via Strange Maps (via Kottke), an interesting project from Rice University measuring the size of ring roads globally…

Strange Maps writes:

In London Orbital, writer, walker and Londoner Iain Sinclair approaches his favourite subject – his home town – by circumambulating it. The book details his trek along the M25, London’s ring road.

Sinclair completes the 117 mile (188 km) journey in 592 pages, which works out to 5 pages per mile (or 3 per kilometer). As ring roads go, London’s is one of the longer ones – which can with some difficulty be gleaned from this map.

The map layers the peripheral highways of 27 of the world’s larger cities onto a poster, designed by the Rice School of Architecture in Houston, TX. That location is no coincidence, because the poster highlights a record for Houston: it has the largest ring road in the world (or at least the largest of all the world cities surveyed).

However, it is unclear how long a book Mr Sinclair would have to write, were he to transplant his peripatetic procedure (and the same distance-to-volume ratio) from London to Houston.

The city at the centre of the US’s sixth-largest metropolitan area (with 5.7 million inhabitants) has three ring roads: Interstate 610 [circling downtown in a 38-mile (61-km) loop], Beltway 8 [about 83 miles, or 137 km] and the as yet unfinished Grand Parkway [State Highway 99].

Clearly, for Houston to have the world’s longest loop, the big black blob on this map could only be the latter. But a few problems arise. Four, to be exact.

One: the Grand Parkway is far from finished. Only two of 11 segments are completed. However tempting it may be, it is hardly fair to tout something as “the world’s largest” before it’s been completed. Especially since, as any large-scale project, the Grand Parkway has its share of detractors. So it might never get done.

Two: even if it is to be completed, plans may change and length might vary. The website for the Grand Parkway Association doesn’t specify beyond the “circumferential scenic highway” going to be “180+ miles” (app. 290 km) long.

Three: the Houston orbital outsizes all others on this map to such an extent that it’s difficult to imagine its circumference to be no larger than London’s by a factor of 180 to 117.

And finally, four: now that I’m mentioning London’s orbital road again — the website for the UK’s Highway Agency states that the M25 is… the longest ring road in the world.

While the identity of the actual highway(s) surrounding Houston and depicted here remains elusive, it is beyond doubt that the Texan city has a large surface, a fact attested by a map posted earlier on this blog (#327), the discussion of which also touches upon the phenomenon of sprawl (large conurbations with relatively low population density) as a result of increased mobility.

Posted on Thursday, May 28th, 2009 at 8:54 am by: Tom Vanderbilt
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The Highway Supply Chain

I’ve been intrigued by the comparisons made to highway traffic behavior and supply chains (see Carlos Daganzo, et al., on the “bullwhip effect”).

A recent article in the Wall Street Journal, on hiccups in supply chains caused by recent economic turmoil, contained a number of implicit, if unstated, comparisons to highway traffic.

The recession has exposed a harsh side effect of the supply-chain system. Because modern industry rewards suppliers with the leanest inventories and fastest reaction times, when economic crisis struck, tech companies up and down the line contracted as sharply as possible in hopes of being the ones to survive.

Forced to guess at demand for their products in a plummeting market, everyone hit the brakes, hard. An examination of the electronics supply chain — from retailers all the way back to makers of factory machinery — shows that, at almost every stage, companies were flying blind as they cut.

The parallel here is a group of cars traveling at high speeds, and close following distances, on the highway — an inherently unstable regime. If one car hits the brakes, the succeeding car, not fully aware from the weak signal how much the vehicle ahead is actually braking (or, for example, if a car’s view of the traffic ahead is blocked by an SUV — for we often make our braking decisions by what drivers further up the chain are doing — the car driver’s “clarity” of the highway supply-chain ahead has been reduced), also hits the brakes — perhaps more than necessary — which amplifies up the chain, often in an erratic fashion. One driver’s underreaction may even penalize another driver six or seven cars up the chain.

And so it is with supply chains:

In March, Best Buy Co. said it could have sold more electronics equipment in the three months ended Feb. 28, but its suppliers’ deep cuts made it tough to keep shelves stocked. Suppliers “all decided to build a lot less,” says Best Buy merchandizing chief Michael Vitelli.

As the contraction raced down the supply chain, its effects became amplified. Rick Tsai, CEO of chip manufacturer Taiwan Semiconductor Manufacturing Co., has said that, in last year’s final quarter, consumer purchases of electronics gear in the U.S. fell 8% from the prior year. But product shipments fell 10%, and shipments of the chips that go into the gear dropped 20%.

Everyone “braked” more than they had to, thus consuming in essence Best Buy’s travel potential.

There was another interesting parallel, in light of a potential economic recovery, and an opening of the supply-chain spigot.

Still, “It’s easier to turn the switch off than turn it back on,” says David Pederson, Zoran’s vice president of corporate marketing.

This has its highway equivalent in the fact, as noted by Dirk Helbing and others, that it takes longer to emerge from a congested state than it does to enter one.

Posted on Thursday, May 21st, 2009 at 8:47 am by: Tom Vanderbilt
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That Old Time Religion

I have come to view Road Use Charging symposia as prayer meetings. We preach to the Converted, whine about Congestion (you should see the pictures!), decry the free-road Infidels, mock the road-building Atheists, re-explain the evident Dogma of Adam Smith’s market economics, and await the messiah of Multimodal Commuting – led by transit and bicycles, of course.

That’s from Bern Grush’s entertaining and illuminating dispatch from TTI’s Symposium on Mileage-Based User Fees.

Posted on Tuesday, April 28th, 2009 at 2:33 pm 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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Ants and Non-Selfish Routing

Faithful readers of Traffic will know of my fascination with the traffic organization of ant colonies. I’ve just been reading a new paper, “Priority rules govern the organization of traffic on foraging trails under crowding conditions in the leaf-cutting ant Atta colombica,” published in a recent issue of The Journal of Experimental Biology, by Audrey Dussutour and colleagues from France’s Université Paul Sabatier.

Dussutour, working with a colony at the University of Illinois, manipulated a bridge on an ant trail so that it was too narrow for two opposing streams of ants to pass abreast. A clear pattern emerged: Ants heading out to the food source always gave way to returning ants that were laden with food (some of which were followed by ants without food). A set of “clusters” emerged, which had its own interesting pattern in same-direction traffic: Even though the ants returning without food were in theory held up by the slower, leaf-carrying ants, those ants still refused to “jostle” past. The results of this strategy were worth noting:

As unladen ants move on average faster than laden ants, these ants were thus forced to decrease their speed. By contrast, this decrease was counterbalanced by the fact that, by staying in a cluster instead of moving in isolation, inbound unladen ants limit the number of head-on encounters with outbound ants. Our analysis shows that the delay induced by these head-on encounters would actually be twice as high as the delay induced by the forced decrease in speed incurred by ants staying in a cluster.

A strategy that appeared to be slower for some individual ants actually benefited the colony as a whole; this is a pattern that often does not hold in human traffic — when, for example, individuals change lanes in unstable traffic, perhaps temporarily improving their own position but having what Benjamin Coifman terms a “butterfly effect” on the lane they have moved into, as well as the one they left.

The French team’s experiment reminded me of a passage from Robert Frank’s book The Economic Naturalist. Frank, based at Cornell, writes about the quaint old one-lane bridges around Ithaca, New York. He notes that a “first come, first served” social norm has emerged at the bridges, so that a stream of steady traffic from one direction wouldn’t hold up cars from the other direction for an undue amount of time. Typically, self-restraint, as in the case of the ants, can help improve overall efficiency.

But when traffic is heavy from both directions, he notes, this norm actually penalizes drivers. As he writes:

“Suppose a ten-car caravan arrived from each direction, with ten seconds separating the cars in each caravan, and with the first driver in the northbound caravan reaching the bridge a split second before his counterpart in the southbound caravan. If no one followed the first-come, first-served norm, all northbound cars would cross the bridge, after which the ten southbound cars would cross. Northbound cars would experience no wait at all, and as readers with a pencil, paper, and a little patience can easily verify, the southbound drivers would experience total combined waiting time of twelve minutes and thirty seconds… In contrast, if all followed the first-come, first-served norm, the first northbound car would cross, followed by the first southbound car, then the second northbound car, followed by the second southbound car, and so on. If you are patient enough to add up the relevant waiting times, you will see the total waiting time would be 80 minutes—37.5 minutes for northbound cars and 42.5 minutes for southbound cars—more than six times as long as when there was no norm.”

Of course, at construction sites and the like, where a flagman is present to wave clusters of vehicles through, this problem does not exist or is mitigated.

I am not sure what the implication of this is. Perhaps we humans simply prize courtesy over rote efficiency (though overall the logic of traffic seems to be that everyone pursues his or her individual efficiency, beyond any impulse towards altruistic politeness). Perhaps it is because we have not evolved to act in concert, as ant colonies have (as Dussutour, et al. note, “ants from the same colony presumably act with a unity of purpose very different to the multiplicity of individual interests pursued by pedestrians or drivers moving in a traffic stream”). Perhaps the Ithaca bridges are simply outmoded in an era of heavy traffic. And on those Ithaca bridges there’s no clear hierarchy of commuters, as in the ant example. But it’s not a stretch to say that a bridge metering system, perhaps inspired by some ant-traffic-derived algorithm, would get people home faster than the traditional way of doing things.

Posted on Wednesday, April 1st, 2009 at 7:58 am by: Tom Vanderbilt
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‘Speed Zone Ahead’ and Other Types of Road Ambiguity

I enjoyed this post from Jeff Sommar on the ambiguity inherent in “Speed Zone Ahead” and other road signs. About “Speed Zone,” he writes: “Reading it at face value, which when you think about it, is how street signs should be read, you would think that the sign is alerting you to the fact that you will be able to speed up in the zone ahead.”

He goes on to mention the sign is used to signal increased speed ahead, as well as decreased speed, which I don’t think is actually true (please confirm, any engineers). But his point about the vagueness is well taken. The sign, after all, doesn’t tell you how much the speed is dropping by (or exactly when). As it turns out, the engineers have heard his cry of confusion, and the sign as pictured above is on the way out, according to some chatter on the MUTCD websites (this site shows some of the new configurations, which are yellow rather than white, and state specific decreases — never increases — in speed). As a side note, there’s also some discussion about what the proper placement is of these signs — so drivers have sufficient time to react and slow before hitting a new speed zone and, perhaps, a speed trap.

The “Speed Zone Ahead” sign brings up another issue of mine, which is the problem of having a road marked for, say, 65 mph, which suddenly hits a stretch that is 35 mph — but the road is exactly the same. The “Speed Zone Ahead” sign is thus a rather weak signal in changing behavior. I think compliance would be higher if, for example, the road were made narrower in the slower section; some alternative paving treatments were introduced; another potential solution is “optical speed zones,” the subject of an article in the latest ITE Journal by Steven Latoski — this treatment uses “bars” painted across the road that diminish in proximity as the driver progresses across them, thus increasing the feeling of speed, thus targeting “an instinctive road user reaction of relaxing the accelerator or adjusting the cruise control.”

I also like Jeff’s mention of the “Dangerous Intersection” sign. Given that signalized intersections account for a very high percentage of traffic crashes, perhaps this should be placed at all intersections. I understand the impulse to put up the sign, at least to provide liability coverage; but is that really all that can be done? And does putting the sign up at one location cause one to lower one’s guard at other areas not so marked? Tricky stuff, this traffic engineering.

Anyone else have favorite examples of signs that gave them pause? My favorite is one that says, simply, “No Traffic Signs.”

Posted on Sunday, March 29th, 2009 at 6:41 pm by: Tom Vanderbilt
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Fairness and Road Funding: Tolls Are Regressive, but Sales Taxes Are More So

One of the first objections to congestion pricing of any sort is the undue burden it would place on lower-income groups (many of these objections seem to come from people who aren’t typically concerned with issues of distributional fairness in other arenas of life).

In “Just Pricing: The Distributional Effects of Congestion Pricing and Sales Taxes,” a paper published in the journal Transportation by USC’s Lisa Schweitzer & UCLA’s Brian D. Taylor, the researchers raise an immediate challenge to this logic: “This contention, however, fails to consider (1) how much low-income residents already pay for transportation in taxes and fees, or (2) how much residents would pay for highway infrastructure under an alternative revenue-generating scheme, such as a sales tax.”

In the paper, they examine the costs on users entailed by Orange County’s S.R. 91, the “value priced” road that allows commuters to choose faster travel times by paying a higher price, against other Orange County roads that are paid for by general sales tax, under Measure M — a more popular way, it turns out, to pay for the county’s “freeways” (an Orwellian abuse of language if there ever was one).

They make a number of important points which I’ll summarize here.

Are tolls regressive? According to this and many previous analyses, yes. But for transport
policy, whether tolls are regressive fails to fully address the justice and fairness issues that
arise in financing road use. Whenever members of lower income groups pay for services,
they may be expected to pay a greater share of their income than do the wealthy. Strictly
speaking, public transit fares are regressive. The fact that congestion tolls are regressive in
the abstract reflects only one aspect of the distributional justice issues facing transportation
and taxation. The real issues are comparative: are congestion tolls more or less regressive
than other tax or price strategies?

On the sales tax, which they note is the fastest growing way to fund roads in the U.S., they note that while sale taxes are distributed widely across society, lower-income groups pay the highest proportion of their income on sales taxes. But here’s the kicker:

While the income regressivity of sales taxes is an issue, it becomes an even greater concern when one notes how much sales tax revenues, when spent on transportation projects that primarily benefit individual users of an improved facility, redistribute cost burdens from users to non-users. In this case, the heaviest users of SR91’s priced lanes—who are the largest beneficiaries of the time savings it provides—are disproportionately from middle- and upper-middle income households both inside and outside of Orange County. While it is beyond the scope of this paper to compare such benefits in detail, we can say that if Orange County’s Measure M had financed the SR91 facility, the added capacity would have lowered the direct time and money costs of peak-hour, peak-direction trips on SR91 in the short term, but resulted in higher aggregate levels of person- and vehicle delay in the longer term if congestion reoccurs. From a regional planning perspective, funding freeway capacity with the sales tax is a pro-auto/pro-driving policy that taxes all residents, the rich and (disproportionately) the poor, to provide benefits to a smaller group of drivers and their passengers.”

This sounds like socialism, Orange County-style: From each regardless of their ability to pay, to each according to their mode of travel.

The sales tax is a “hidden” subsidy that makes driving seem cheaper than it is (and thus never encourages any reduction in driving). And on that subject let’s not forget the semi-permanent “gas tax holiday” the U.S. has been on for nearly the last two decades. As Taylor notes elsewhere (pdf here), “the average combined state/federal fuel tax in the United States today ($0.375 per gallon) charges drivers about $0.02 per miles, on average, for their use of the road system, the lowest rate in the developed world, and about one-third of the inflation-adjusted U.S. rate in 1960.”

The result is ever more drivers using ever worsening roads. The U.S. road transportation system in this regard reminds me of the old Catskills joke, noted in Annie Hall: “Boy, the food at this place is really terrible.” The other one says, “Yeah, I know; and such small portions.”

And going back to Orange County and Measure M, let’s not forget the question of externalities.

These problems are especially a concern if the environmental, energy, safety, and congestion externalities associated with driving are also regressively distributed (Schweitzer and Valenzuela Jr. 2004). If these externalities are, in fact, regressively distributed, then the Measure M transportation sales tax, if used on road projects, would disproportionately tax poorer residents to subsidize an activity whose externalities (such as noise and freeway-adjacent particulate emissions) harm them.

Posted on Friday, March 27th, 2009 at 8:10 am 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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The Hidden Benefits of HOV Lanes

HOV, or “carpool” lanes, are, like everything, the subject of much controversy in the world of traffic. Do they make congestion worse for everyone while only aiding a few? Do they cause more crashes? Needless to say, I could have written a book only on the complexities of the Diamond Lanes (though I’m not sure who would want to read it).

A new paper, “The Smoothing Effect on Freeway Bottlenecks: Experimental Verification and Theoretical Implications,” from Michael J. Cassidy, Kitae Jung, and Carlos F. Daganzo at the University of California-Berkeley, presented at last week’s TRB (I’ll be data-mining the huge trove of research from that conference over the coming weeks), suggests that HOV lanes can provide overall benefits to highway traffic flow — even when the lane itself is underutilized. As with many things about traffic flow, this is beyond the grasp of the average driver, who may simply look over at the HOV lane, see that fewer cars are in it than his own (even if, of course, they’re carrying more people), and begin to grouse about misguided government policy.

The authors looked at a particular stretch of California freeway with a regularly occurring bottleneck, essentially a “merge bottleneck” resulting from increased volumes of entering traffic. A carpool lane becomes active during the morning and evening rushes; and one might be led to think the activation of the lane somehow causes the bottleneck. But the authors note, “previous analysis established that the carpool lane did not contribute to the bottleneck formation and capacity drop. Instead, and as is typical of merge bottlenecks without carpool lanes, the queue first formed in the shoulder lane and then spread to all lanes.” But even as the capacity of the carpool lane began to drop, the researchers observed an interesting pattern: The “discharge” of vehicles from the bottleneck in other lanes actually began to increase.

They looked at video footage, taken from a pedestrian overpass, to figure out what was going on. Interestingly, it was all about changing lanes. In lane 2, as pictured above (the one next to the HOV), drivers made fewer changes in and out of it when the carpool lane was activated (some of those drivers may have previously been jumping back and forth between lane 1, the ‘fast lane,’ and 2).

And here’s where it gets really interesting:

The same phenomenon was observed a few minutes earlier in lane 3, as drivers started
anticipating the impending carpool restriction. The video data reveal that: (i) drivers’ tendencies to avoid the median (carpool) lane as its activation time approached created crowded conditions in adjacent lane 2, starting at about 14:52 hrs; and (ii) although this crowding temporarily induced some drivers to migrate to lane 3, its more significant impact was to dampen the entries made into lane 2 from lane 3; (see Cassidy, et al, 2008). The net result: lane-changing maneuvers between lanes 2 and 3 diminished at 14:52 hrs, as revealed by the boldfaced oblique cumulative curve in Fig. 5. As in the case of lane 2, this reduction in lane changing was accompanied by a sudden and sustained increase in lane 3’s discharge flow.

The authors observed what they called a “smoothing effect.” Drivers were less tempted to change lanes, because there were fewer options available, and the “discharge flows” actually increased. When the carpool lane wasn’t activated, lanes saw anywhere from 9% to 13% worse performance in VPH (vehicles per hour). When considered in terms of “people hours traveled,” the activation of the carpool lane provided a benefit on the order of 30%. The authors note that if this “smoothing effect” is not observed and quantified, long highway delays might be incorrectly attributed to the carpool lane.

What’s interesting about this is that for many of those individual drivers, they were presumably changing lanes to try and improve their own position. But in doing so they were actually reducing the overall performance of the highway.

As the authors note, it’s worth investigating how signage and striping might reduce “disruptive” lane changing. “Disruptive lane changing,” they add, “might also be reduced in some cases by sorting drivers (and vehicle classes) across lanes according to their preferred travel speeds; or in other cases by inducing a more even distribution of flows across lanes.”) We already have seen “variable speed limits” to help smooth out flow in a linear sense; maybe someday we’ll have “variable lane assignment” to smooth it out across the highway.

Posted on Monday, January 19th, 2009 at 11:24 am by: Tom Vanderbilt
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Art That Stops Traffic (or Traffic That Stops at Art?)

I was listening last night to Frances Anderton’s interview with agit-prop artist Robbie Conal on KCRW’s Design and Architecture and was quite surprised to hear, out of nowhere, a discussion of traffic lights.

Why? Because, Conal noted, at every intersection in L.A. there are controller boxes for the traffic signals — “virulent spawn of HAL” — I think he said. These, it turns out, make perfect surfaces for displaying things like posters. So Conal, when he was starting up, went out and actually measured the dimensions of these boxes, and created appropriately sized posters (also using Helvetica Bold so that it could be read by drivers). He noted that if a driver missed one at a certain intersection, he could serially repeat them at a number of intersections so he’d be guaranteed a viewing (depending on the cycle timing!)

This makes Conal, I suppose, LADOT’s unofficial ‘artist in residence.’

Posted on Thursday, October 30th, 2008 at 3:13 pm by: Tom Vanderbilt
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Obsessive Traffic Photo Studies

Two recent entries have crossed my desk. One, from Martin Parr, who I interviewed some years back. Parr, who makes the banal seem lurid, and vice versa, turns his lens now on the humble parking space. Pictured at right is Mexico City, home of course to the famous “viene viene” boys, who hang around street corners and wave drivers into spots that they’ve secured with chairs, as pictured.

The description for Parking Spaces reads so:

“Between 2002 and 2007, Martin Parr photographed ‘the last parking space’ available in 41 countries – somewhere you could have parked your car, had you been there at the time. Using a compact camera, and driven by wanting to express “the individual frustration of finding somewhere to park, but on a global level”, this is the latest body of work in Martin’s methodical personal address to the issues of globalisation – the desire for a precious parking space being a banal unifier of the middle classes the world over.”

Meanwhile, the always interesting Mikael Colville-Andersen over at Copenhagenize has contributed Stripey Streetness, which, as the description notes:

“A splendid photo series about the zebra crossing as an instantly recognisable symbol in the urban landscape. 130 photographs from 10 countries celebrating that striped zone created in order to keep people out of harm’s way by providing safe passage across city streets. Painted bridges that guide the bustling masses of pedestrians through a city. The zebra crossing is not a destination it itself but it is an important tool in getting yourself from A to B. It funnels all types of people together into one space, for a few brief minutes of togetherness. We are strangers but while waiting for the light to change and for those dozen or so steps through the zone we are in a flock. This photo series shows city life and city people framed within the zebra crossing. People coming and going and waiting. All of them telling us stories with their body language. Wide strides or short steps. Hunched shoulders or head held high. The zebra crossing becomes a stage on which people around the world are brought together.”

Not sure if he’s got Shibuya in there…

Posted on Tuesday, October 21st, 2008 at 5:06 pm by: Tom Vanderbilt
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So Many Ways to Stop in Canada

As just a short note following up on my comments on Montreal’s strange “Stop” signs, another thing to note of course is the linguistic variation. I’ve just returned from the Westmount region of the city, where the signs are in English (as in the one posted below, which, as notes, seems a bit odd since the English bit on the street signs has been blacked out).

But one also seems to find bilingual English/French, as well as signs in Mohawk, Inuktitut, and Kahnawake — there may be more. In any case, an interesting reminder of how culture trickles into the standardized regime of traffic safety.

Posted on Monday, October 13th, 2008 at 5:14 pm by: Tom Vanderbilt
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Montreal’s Curious Stop Signs

I was struck by these “arret” signs in Montreal, which have an additional sign informing the driver of which other roadways have a stop sign. In theory, I suppose, this is meant to be a good thing, giving the driver information as to who will be stopping, etc.

But there are a few problems. The first is that it took me a few weeks to even notice the supplementary information. The second is that often the sign is just providing redundant information (informing the driver, on say, a one-way street that the opposing street will not be stopping — but of course there will be no oncoming traffic as it’s one-way!). The third, as you can see in the photo, is that it just adds more information to an already complex and quite garish bouquet of warnings.

But the most objectionable thing about these signs is that they exist at all. These are scattered all over “Vieux Montreal,” which has a warren of narrow, pre-automobile streets, with an abundance of pedestrians and cyclists (and horse-drawn carriages). Drivers should be looking at the streets, looking around, not glancing up at a sign to discern who will be stopping and who won’t (that is, if they obey the sign in the first place).

Posted on Saturday, October 11th, 2008 at 10:23 am by: Tom Vanderbilt
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The Car Capital of the World Is…


As per the just-arrived Pocket World in Figures, from The Economist, the Grand Duchy has the most cars per 1,000 population: 647. (Also a bit improbably, Iceland is second).

Ethiopia claims the lowest rate, tied with Rwanda, with 1 car per 1000.

As an example of the sometime skewed relationship between car ownership and safety (as per Smeed’s Law), Botswana, which has just 42 cars per 1000 residents, is No. 1 in terms of traffic fatalities per 100,000 inhabitants (with 30).

The strangest figure to my mind was the “most injured in road accidents” column. The leader, by far, was Qatar, with 9,989 per 100,000 population. OK, so it also seems have to the most crowded road networks. But still, its injury rate (for a place where alcohol consumption is presumably lower) seems off the charts — its near neighbor, the UAE, for example, has just 183 (maybe the Qatari police are just really good at reporting).

Or is it something else? I do know that the Qataris are terrible when it comes to seat-belt wearing rates. Any other theories/facts/experiences?

Posted on Thursday, September 18th, 2008 at 12:31 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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