Archive for the ‘Traffic Engineering’ Category

Over at Politico, I offer an appreciation of the aerial photographs of highway interchanges by the Canadian photographer Peter Andrew.

“What is it that makes the patterns of highway interchanges so captivating? Perhaps we are drawn in by our pattern-hungry brains, mentally tracing the loops and parabolas, looking for connections and symmetries. Perhaps we gain a pleasurable synaptic charge from mastering the routes. Or, in the way the contours of Jackson Pollock’s drip paintings have been shown to follow a strongly fractal logic, perhaps a well-designed highway interchange hits some kind of subconscious geometric sweet spot. (Long before highways, braided knots were figuring into various religious symbologies, and Pictish knot imagery from the Book of Kells seems curiously evocative of modern day interchanges.)”

Via Copenhagenize.

Starting today in Slate, I take a four-part look at walking, the “forgotten transportation mode,” in America and elsewhere.

Simply by going out for a walk, I had become a strange being, studied by engineers, inhabiting environments whose physical features are determined by a rulebook-enshrined average 3 foot-per-second walking speed, my rights codified by signs. (Why not just write: “Stop for People”?) On those same signs in Savannah were often attached additional signs, advising drivers not to give to panhandlers (and to call 911 if physically intimidated), subtly equating walking with being exposed to an urban menace—or perhaps being the menace. Having taken all this information in, we would gingerly step into the marked crosswalk, that declaration of rights in paint, and try to gauge whether approaching vehicles would yield. They typically did not. Even in one of America’s most “pedestrian-friendly” cities—a seemingly innocent phrase that itself suddenly seemed strange to me—one was always in danger of being relegated to a footnote.

Which is what walking in America has become: An act dwelling in the margins, an almost hidden narrative running beneath the main vehicular text. Indeed, the semantics of the term pedestrian would be a mere curiosity, but for one fact: America is a country that has forgotten how to walk. Witness, for example, the existence of “Everybody Walk!,” the “Campaign to Get America Walking” (one of a number of such initiatives). While its aims are entirely legitimate, its motives no doubt earnest, the idea that that we, this species that first hoisted itself into the world of bipedalism nearly 4 million years ago—for reasons that are still debated—should now need “walking tips,” have to make “walking plans” or use a “mobile app” to “discover” walking trails near us or build our “walking histories,” strikes me as a world-historical tragedy.

My latest Slate column explores the concept of “rolling speed harmonization” on a Colorado highway.

As one report describes it, speed harmonization “holds that by encouraging speed compliance and reducing speed differential between vehicles, volume throughput can be maximized without a physical increase in roadway dimensions.”

The concept plays, in part, on one of traffic engineering’s core truths: Big speed differentials are dangerous. This is laid out in the “Green Book,” the bible of the American Association of Surface Highway Transportation Officials. “Crashes are not related as much to speed as to the range in speeds from the highest to lowest,” the book states. “Studies show that, regardless of the average speed on the highway, the more a vehicle deviates from the average speed, the greater its chances of becoming involved in a crash.”

I joined the stable again over at the New York Times’ Room for Debate, this time on the idea of full highway shutdowns.

Just for historical curiosity, here’s my original, somewhat more fanciful (but contextual) submission:

It’s perhaps appropriate that the town that produced Michael Bay should summon such a bombastic bout of overblown apocalyptic fury as the forthcoming “carmaggedon.” Given the life-support functions of the 405 in the L.A. region’s transportation monoculture, perhaps the hype is warranted, but the truth is, highways are closed all the time, and there’s been much study and practice into how to do it most effectively.

The perturbed driver may be asking, ‘why do they have to close the whole thing down? Why can’t they just do it a lane at a time?’ And indeed, any number of strategies have been tried to mitigate traffic impacts during construction, from nocturnal work crews (which has been found to add 6% to the base price of a project) to various incentive plans for road contractors.

But as research by the Federal Highway Administration has shown, closing down a highway entirely means the job gets done, on average, 63 to 95 percent faster than projects that tried to maintain a semblance of traditional traffic. Why? No traffic means no interference from drivers, no work-zone crashes (in 2007, for example, 835 people were killed in work zone crashes) or other bad behavior, not to mention that the trucks hauling materials and workers don’t have to sit in the same congestion as everyone else as they go back and forth.

The secret to making this happen, as is happening in Los Angeles, is to enact a comprehensive “Traffic Management Plan,” with careful study of alternate routes and “network effects.” Implicit in this is to issue a prediction of Nostradamusian direness; to do for weekend driving what Jaws did for ocean swimming (“just when you thought it was safe to go to Santa Monica”).

This reason this generally works is that in any road system, there is a certain amount of elasticity; not every driver on that road has to be there at that time. There may be another route, another mode of travel. Or they just stay home. When highway segments are taken out because of disaster (as in the Minneapolis I-35 W bridge collapse, or the collapse of Manhattan’s West Side Highway) the surrounding roads do not automatically filled up with all the diverted drivers; rather, some traffic “disappears.” To quote two of the main findings of a report analyzing any number of road closures, planned or otherwise, by transport researcher Phil Goodwin and colleagues: “When roadspace for cars is reallocated, traffic problems are usually far less serious than predicted” and “Traffic reduction is partly explained by recognizing that people react to a change in road conditions in much more complex ways than has traditionally been assumed in traffic models.”

When Los Angeles partially closed the 710 expressway for eight weekends, it was able to reduce traffic by 37%. Interestingly, though, traffic was lowest through the work zones the first weekend, and then grew gradually on each successive weekend, as L.A. drivers, in a kind of city-wide learning curve, began testing the drive. In the case of the 405 closure, of course, drivers won’t have that option. There’s no knowing how bad or how good it’s going to be, until you’re in it.

On the off chance you missed, me and some other fuzzy headed Jane Jacobs types, a tenured suburbanite urbanist or two, as well as a few random tar-breathing asphalt heads, discuss, in the paper of record, the idea of bringing some European-style traffic demand management to U.S. shores. The pyrotechnics are to be found here.

3-Way Street from ronconcocacola on Vimeo.

Via http://blog.ronconcocacola.com/

As discussed in Traffic, sometimes the best way to eliminate tension over ‘late merging’ is to simply eliminate the concept, as the Illinois DOT seems about to do.

“Once people get used to it, it seems to work well,” Wegmeyer said. “As long as traffic alternates at the merger, it should go more smoothly.”

Of course, that “as long as” still presents challenges, as those people in the “open lane” may still feel some sense of priority over those they view as late-arriving interlopers.

(thanks Darrin)

I am glad that my posting on the Prospect Park West bike lanes occasioned a serious and thoughtful response (see the comments).

I wanted to reply to a few points.

They write:

(1) PPW is not simply an arterial roadway between intersecting streets (as is the adjacent roadway inside Prospect Park, which, we have argued, would be a more appropriate location for a two-way bike lane). Rather, PPW borders high-density residential blocks—with a school and elder-care facility (on one side of the street) and entrances to Prospect Park (on the other). This means that on a less-than-one-mile stretch of roadway, thousands of residents and park-goers are continuously entering or exiting school buses, wheel-chair vans, taxis, or driveways, while dozens of Fresh Direct, UPS, Fedex, USPS trucks, moving vans, and other delivery vehicles are also blocking one of the two remaining traffic lanes. This requires that drivers in the blocked lane continuously shift into a single more-heavily-used traffic lane to avoid the blockage. And since this single lane is now narrower on a significant stretch of PPW, if not the entire street (as our measurements, pace Vanderbilt’s assertion to the contrary, clearly show), there is less margin to avoid car doors opening, drivers or passengers squeezing into their vehicles, parents lifting babies from their car-seats, cars edging into or out of parking spots, or side view mirrors extending from vehicles. These circumstances, rather than producing a “calming feeling,” are more likely to produce irritated impatience, at best.

I admit that the studies I referred to are for road types different from PPW; in part this is a necessity because of the rather unique nature of PPW itself. But I am interested here in their description of all the exiting school buses, UPS trucks, parents getting babies out of cars, Fresh Direct vans, etc. Given this huge amount of stopped traffic, and pedestrian activity, to my mind the most important safety benefit we could bring to those users is a reduction of the speeds on that street — which were typically well above the speed limit prior to the installation of the bike lane. Speed, and the violating of right of way — not lane changing and merging — is the root cause of the vast majority of serious traffic injury in New York City. As I’ve said repeatedly, drivers, in their ‘irritated impatience,’ have tended to use PPW as a high speed arterial to neighborhoods beyond Park Slope rather than the neighborhood street it should be. I will take an infinite number of bent mirrors over the lives or health of any one person.

In their second point, they note:

“In addition to the option of moving the lane onto the adjacent roadway inside the park, making the PPW bike-lane one-way is the other proposal we have made as members of “Neighbors for Better Bike Lanes.”

I would take a one-way bike lane over no bike lane; but as a condition of that one-way status, I would call for a protected one-way bike lane, in the other direction, on Eighth Avenue, which suffers from some of the same speed problems as PPW.

They then note:

(1) Vanderbilt’s basic argument relies on the perception of increased safety that roadway users (drivers, bikers, and pedestrians) may have when more drivers and riders are using fewer and narrower lanes, because their awareness of other roadway users is heightened. But this perception of increased safety is not what users of PPW have experienced. In a self-selected survey of over 3,000 Brooklynites conducted by Councilmembers Lander and Levin, most people—bikers were the only exception—reported feeling less safe after the bike lane was installed (Ref. 2).

This misrepresents what I have said, and indeed highlights a problem: Perception of safety and actual safety in traffic are not always the same. When subjects have been asked to identify what they think are crash hot spots in certain locations, for example, they often choose places with low numbers of crashes, not the actual hot spots. When roundabouts are installed, it’s quite common for the local populace to protest that their safety has been compromised — when in fact, roundabouts, as have been documented in any number of studies, tend to make things safer for all road users. ‘Shared space’ experiments in Europe and the U.K. have shown a similar disconnect between perceived and actual safety.

But let’s stick to what we know: The actual numbers from PPW, which are now available, via the Brooklyn Paper:

“Crashes are down from an average of 30 in six months to 25, or 16 percent.

• Crashes that cause injuries are down from 5.3 in six months to two, a whopping 63-percent drop.

• Before the project, a crash was twice as likely to include an injury.

• Injuries to all street users dropped 21 percent.

The data also found that since the lane was installed last June, there have been no reported pedestrian injuries and no pedestrian or cyclist injuries from pedestrian-bike crashes.”

Granted, crashes involving pedestrians and bicycles tend to be underreported, but vehicle crashes, particularly involving injury, are not — and by this measure, the addition of the lanes has actually made for a safer environment for all road users. An increase in active transportation; a decrease in injury — I fail to see this as a problem.

From somewhere in Germany, I believe (would be curious to know the exact location), a roundabout with nothing in the center save paint. I’d be curious about the stats for this intersection; on the whole it seems more or less orderly (there’s confusion but low-speed confusion), but some people just seem to blow straight through as if they had a green light in a signalized intersection.

My latest Slate column looks at two transportation forms, the monorail and the streetcar, each with their supporters and each with their detractors, and how time’s arrow seems to have inverted somewhere along the way:

What’s interesting about Disney World and Disneyland is not merely the range of transportation options, but the mixture of new and old modes they represent. These varied ways to get around reflect biographer Neal Gabler’s observation that Walt Disney was “at once a nostalgist and a futurist, a conservative and visionary.” One imagines he would have been equally happy riding the retro trolley on Main Street as whisking through Tomorrowland in an ultramodern monorail.

So the future we thought we were going to get somehow seems antiquated, while the past looks increasingly, well, futuristic. Why is the trolley ascendant as the monorail declines?

[P.S. I do realize a fair number of people prefer buses to either of these options, but for space it was cut. An original line read: “Light-rail supporters — and transportation people, whether for reasons of funding, fandom, or something else, and even if they’re working toward similar goals, tend to cleave into camps (a third group, the bus people, find their vessel of choice superior to both the light-rail and monorails) — counter with a battery of well-practiced rejoinders…”]

There was an assertion made in one of the letters (signed by Louise Hainline, Norman Steisel, and Iris Weinshall in response to a recent New York Times editorial on cycling that caught my eye:

When new bike lanes force the same volume of cars and trucks into fewer and narrower traffic lanes, the potential for accidents between cars, trucks and pedestrians goes up rather than down. At Prospect Park West in Brooklyn, for instance, where a two-way bike lane was put in last summer, our eyewitness reports show collisions of one sort or another to be on pace to be triple the former annual rates.

The first point is that while the PPW conversion did take away one travel lane, the width of the existing lanes was not altered. So there may be fewer lanes, but they are not, as the letter argues, “narrower.” It may be that entire street feels narrower, which, as an emerging school of what I’ll call ‘behavioral traffic calming’ argues, is actually a good thing. Drivers, as I’ve quoted Ezra Hauer as saying, “adapt to the road they see.” They either do not see traffic signs or fail to read their meaning correctly. If they see a wide open, long boulevard, they will drive like this.

Even if the lanes were narrowed, as John LaPlante recently argued in the journal of the Institute for Transportation Engineers, “there is no significant crash difference between 10-, 11-, and 12-foot lanes on urban arterials where the speed limit is 45 mph (or less).” (a finding, he notes, that was unfortunately left out of AASHTO’s recent Highway Safety Manual).

And there’s something deeply suspicious about that “eyewitness reports” note; were they actually out there, day after day, meticulously logging conflicts and crashes (tellingly, they make no note of severity)? And why, if everything was so great with the street before, were they even doing these “before” counts? As the case of roundabouts shows, what people perceive as individual danger often does not translate at all to an increase in overall risk; in fact, it’s quite the opposite.

But let’s take that notion — that fewer and narrower lanes lead to more crashes. This is a staple of traffic engineering, and in fact it does have some validity — when applied to highway environments (which PPW at times unintentionally resembles). Even here, though, the effects are often not ‘statistically significant’ and ‘more complex than expected.’

But in non-highway environments, there’s all kind of evidence that reducing the number of lanes (a.k.a. the ‘road diet’) can have positive safety benefits. As the Federal Highway Administration has noted:

Road­ diets­ can­ offer­ benefits ­to­ both ­drivers ­and­ pedestrians… road diets may reduce vehicles speeds and vehicle interactions, which could potentially reduce the number and severity of vehicle-to-vehicle crashes. Road diets can also help pedestrians by creating fewer lanes of traffic to cross and by reducing vehicle speeds. A 2001 study found a reduction in pedestrian crashing risk when crossing two-and three-lane roads compared to roads with four or more lanes.

But what if one of those lanes your crossing is a bike lane? Surely that must make things less safe, no? More interactions in less space. In a forthcoming paper to be published in the Journal of Environmental Practice Norman Garrick and Wesley Marshall examined 24 California cities (12 with relatively low traffic fatality rates, 12 with relatively high rates). They found that the cities that had a higher bicycle usage had a better safety rate, not just for cyclists but all road users. They write:

Our results consistently show that, in terms of street network design, high intersection density appears to be related to much lower crash severities. Our street design data also contains strong indications of these trends; for example, the high biking cities tend to have more bike lanes, fewer traffic lanes, and more on-street parking. At the same time, large numbers of bicycle users might also help shift the overall dynamics of the street environment – perhaps by lowering vehicle speeds but also by increasing driver awareness – toward a safer and more sustainable transportation system for all road users.

And as Eric Dumbaugh, of the University of Texas A&M, notes, “most recent research reports that wider lanes on urban streets have little or no safety benefit, at least to the extent that safety is measured in terms of empirical observations of crash incidence” (e.g., Potts, I.B., Harwood, D.F., & Richard, K.R. (2007). Relationship of Lane Width to Safety for Urban and Suburban Arterials. Transportation Research Board 2007 Annual Meeting; Milton, J., & Mannering, F. (1998). The relationship among highway geometries, traffic-related elements and motor-vehicle accident frequencies. Transportation 25, 395–413; and so on).

But the authors of this letter are not trafficking in empirical evidence, even as they allege that the NYC DOT’s data “more puzzlement than enlightenment.” It’s unfortunate that this letter is signed by a former DOT commissioner, and an academic — who should both know that it is evidence and analysis, not vague “eyewitness” reports and random testimony, upon which good science, planning, and safety interventions are made.

And as always, curious to hear of more work either supporting or countering what I’ve said here.

I have a short piece in the current World Policy Journal in response to the question of the future of the city. In this telegraphic dispatch I addressed the place of the car in the city (N.B.: The piece could also be headlined: ‘An Open Letter to Marty Markowitz’):

We spent much of the twentieth century engaged in a campaign to retrofit our cities to the car. However much this may have seemed to make sense at the time, it now looks more like a misdirected effort to save the city by destroying it. As plentiful as the benefits of individual vehicular mobility may be, the large metropolis can never comfortably accommodate any more than a fraction of its citizens in this manner, and we have learned the consequences of trying to do so. Ever-lengthening commutes have meant degraded public spaces, negative health outcomes, social fragmentation, infrastructure whose maintenance goes underfunded.

In the city of the future, we need to pursue policies that allow for safe, efficient and affordable transport of the many, while recognizing that market-based approaches that so rationally apportion space in the private sector can and should be applied to the valuable urban space — in the form of roads and parking spaces—that cities essentially give away. We need to recognize that streets are public spaces too, and not merely, in the old view of 1930s utopian modernism, channels for moving as many vehicles as quickly as possible. The car will continue to exist, but should be treated as a “renter” of the city, not its landlord. The urban car of the future should be shared, smaller, and slower.

Via ENR, an interesting piece on tunnels, shockwaves, and traffic psychology.

“If everybody goes the same speed and distance and nobody uses the brakes, you can through-put more vehicles,” Khattak said.

“We’ve tried to counter this whole perception that you’re driving into a hole in the water… so you don’t feel like you’re going into a different environment than you’re coming from,” said Dwayne Cook, regional operations manager for the Virginia Department of Transportation.

It took me a long time to, er, come around to the logic and efficacy (at least in safety terms) of the Jersey Jughandle, but following a prompt from Anthony Townsend, do any NJ DOT readers or likewise know how the Garden State came to be the leader in this somewhat rare infrastructural form? Taking a stab I’d say it had something to do with the state’s density and preponderance of highways, but can anyone elucidate us beyond that; e.g., the name of the inventor, etc.

No time to comment on this as, coincidentally, I’m about to leave for the Netherlands, but Bern Grush sifts through the ashes.

A colleague sends the above photo of a “double roundabout,” in Buffalo, NY (or it’s suburbs). While your first thought might be, wow, how confusing, consider the Google Map image below that shows the original intersection — too big, actually two intersections masquerading as one (one can imagine cars getting “trapped” in that little extra segment, and box-blocking problems). Undoubtedly there was a crash problem, hence the double roundabout. Which are used in the U.K. (and taken to its logical extension in the “Magic Roundabout”, of course, but are, as far as I know, relatively novel here. Anyone live near here by chance and care to weigh in?

(thanks Nate)

An interesting prototype design via the PFSK Conference for an “ergonomic” crosswalk that takes into account pedestrians’ natural inclinations to want to shorten the distance it takes them to cross the street (as someone once told me, ‘pedestrians are natural Pythagoreans’). I can foresee a problem with cars, who already stray into the crosswalk, having a bit of a problem lining up. And while I like the red/yellow LED light concept in theory, does it just lessen our tendency to look at the actual environment for safety cues?

Over at KCRW’s Design and Architecture, Francis Anderton considers a part of the built environment often overlooked in transportation questions: Shade. It is remarked that trees in Los Angeles are placed to provide shade for cars, not people walking on sidewalks.

The New York Times notes:

India overtook China to top the world in road fatalities in 2006 and has continued to pull steadily ahead, despite a heavily agrarian population, fewer people than China and far fewer cars than many Western countries.

It goes on to cite a few reasons:

A lethal brew of poor road planning, inadequate law enforcement, a surge in trucks and cars, and a flood of untrained drivers have made India the world’s road death capital. As the country’s fast-growing economy and huge population raise its importance on the world stage, the rising toll is a reminder that the government still struggles to keep its more than a billion people safe.

In China, by contrast, which has undergone an auto boom of its own, official figures for road deaths have been falling for much of the past decade, to 73,500 in 2008, as new highways segregate cars from pedestrians, tractors and other slow-moving traffic, and the government cracks down on drunken driving and other violations.

As R.J. Smeed first noted, having fewer cars is by no means an indicator that one will have fewer traffic fatalities (and an important distinction in the developing world is that traffic fatality categories are topped by pedestrian deaths). But one thing that goes unmentioned in the piece is research, cited in Traffic, by Elizabeth Kopits and Maureen Cropper, that links a nation’s rate of traffic fatalities to its GDP. When GDP climbed from $1200 to $4400 in the countries studied, the fatality rate dropped by a factor of three.

According to the CIA Factbook, the 2009 estimated GDP of China was $6600, while in India it was $3100. Just by this measure alone, the discrepancy between the two countries could be predicted, if not fully explained (for there would be many other factors at play here, like culture, governmental structure, etc.). It’s not hard to imagine why higher GDP would lead to fewer deaths (in this regard it’s not properly correct to call traffic deaths, as is often done, a “disease of affluence”); as development levels increase, there’s not only more money for engineering, enforcement, etc., but also a reduced likelihood of corruption (roads are built to standards, police less willing to take bribes), accompanied by a greater societal emphasis in safety in all kinds of areas of life. But the real question is how India can close the huge fatality gap with China even if it can’t immediately narrow the GDP gap.