CONTACTTRAFFICABOUT TOM VANDERBILTOTHER WRITING CONTACT ABOUT THE BOOK

The Caldecott Tunnel Problem

Mergers and Disquisitions

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

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

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

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

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

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

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

The New York Times
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August 3, 2008
The Urge to Merge
By CYNTHIA GORNEY

HERE IS THE CALDECOTT TUNNEL PROBLEM. If there’s another person with you right now, you may end up raising your voices as you consider it. I’m just warning, is all. The last time I brought up the Caldecott Tunnel Problem among friends, two people who had been a happy couple for a long time started arguing, and then they looked at each other as if something new and disturbing were presenting itself, and when I got up to go, one of them was pounding the table and yelling at her beloved, “But that is so wrong!”

Anyway, the problem. Near where I live, which happens to be Northern California but that’s not relevant, there’s a three-bore tunnel that runs east-west under some steep hills that separate the suburbs (east) from Oakland and Berkeley and eventually San Francisco (west). If you’re driving east-west around here, you use the Caldecott Tunnel; you could go winding over the hills and bypass the problem altogether, but it would take forever and you don’t want to. The freeway leading to the Caldecott is called Highway 24, and on the suburban side of the tunnel it courses like a river beneath open sloping grassland, all golden and Tuscan right now in summer.

So here you are, let us say, heading west toward the Caldecott at the end of a July afternoon. The geography, what with the hills rising on either side, pretty much requires you to focus on the thing that is about to happen in front of you — you can see it coming, and sometimes from quite a distance, depending on how bad the backup is. The trick about the Caldecott is that although each bore is two lanes wide, the middle bore switches direction, by means of signage and mechanically raised cone separators, contingent on the flow of the main morning and evening commute. So if you’re driving out of the suburbs toward Oakland at the end of the day, the cars coming the opposite way take that middle bore, which means your side of 24 is being coned off into the one remaining bore on the right — a four-lane to a two-lane funnel.

This is the point at which the North American driving populace, as you know, cleaves into two camps.

Two-thirds of us, according to calculations I have made while brooding inordinately about this inside my Subaru, are lineuppers, slowing rapidly from 70 to 30 or 20 or whatever and taking our places — courteously and patiently, as our mothers taught us to do, respecting the broad tenets of social justice and the primacy of fairness to all persons on the road, regardless of income or ethnicity or car model or perceived level of personal importance — where was I? Oh. Sorry. Taking our places at the end of the line, I was saying, the long two-lane line that has formed to the right, creeping toward the mouth of our tunnel bore. There is still some empty lane space beside us on the left, true, where the cones are gradually closing those left lanes down. But people are already lined up. If we passed them on the left to get in farther ahead, we would be cutting the line.

One third of us, on the other hand, zoom on by. For purposes of this problem, I shall call these sidezoomers. (When I raised the Caldecott Tunnel Problem with my father, who is 83, he startled me by suggesting a longer label that included more bad words than I believe I have ever heard him use at one time.) Sidezoomers have a variety of strategies, each exaggerated by the configuration of the Caldecott but replicated in bottlenecks across the land: there are the ones who zoom by a few dozen cars, angling in when they see a plausible opening; and there are the ones who zoom all the way up, to the very top of the cone-off funnel, at which point they thrust their aggressive little self-entitled fenders toward the lineup and nudge themselves in. And there are those who opt for frontage-road sidezooming, which requires maneuvering into the far-right highway lane in order to get off at a certain pretunnel exit that dumps cars onto a surface street alongside Highway 24. They zip along that street and get back on 24 at the next entrance, slipping in ahead of the bumper-to-bumper highway lineup they just bypassed. So now they’re cutting the line, too, but from the right.

And that very last exit lane before the tunnel, also on the right? You can’t get back onto the highway once you’ve exited there, but if you’re a sidezoomer you can slide into the empty exit-only lane, still on the highway but pretending you’re leaving, and then you drive and drive right past all the lineuppers until whoops, now at the last minute you’ve changed your mind and you’re not exiting at all; you’re sneaking back into the line.

Not in front of me, though.

Until recently, I had the idea that I was somewhat overwrought about this. I supposed there were not all that many drivers gritting their teeth behind their steering wheels, practicing what Jerry Seinfeld once called the stare-ahead, while declining to let the sidezoomers in and musing at the same time that this is the problem with modern American capitalism, really, this anti-aristocratic all-men-are-created-equal narrative we pretend to cherish while simultaneously celebrating the individual’s right to do whatever advances his own interests without technically breaking the law, Gordon Gekko triumphant over Cesar Chavez, and that is an exit-only lane, you rodent, so no, you are not cutting in front of me unless you look as if you might have a gun in your car, in which case, O.K., but you’re still a rodent.

I was mistaken, as it turns out. There are a lot of people who feel this way.

I know this because a while ago I began asking around — politely, I mean, trying to avoid words like “bullying” and “lowlife,” making inquiries as to who lines up at bottlenecks and who sidezooms. The truth is, I had come to be a tiny bit rattled by uncertainty. I kept studying that empty lane space on either side of our lineup. Something about the physics was not working out. I bought a textbook called “Traffic Flow Fundamentals,” hoping for instructions as to the technically correct way to enter a lane-drop funnel, but the explanations looked like this:

When k = kj,µ = 0 (vehicles bumper to bumper but no movement):

0 = α0 1n (C2/kj)

So I started consulting professionals on my own: traffic engineers, the highway police, queuing theorists. The learning curve, it must be said, was robust. I hadn’t known queuing had theories. But of course it does, mathematicians and business-operations people have to work them out, the heart-attack patient gets in ahead of the sprained ankle and nobody has a problem with that, and anybody who has been to Europe intuitively understands what one engineer meant when in midsentence he said to me, “perfect England,” meaning culturally mandated compulsive queuing, and, “perfect Italy,” meaning culturally mandated compulsive nonqueuing. I learned about the father of modern queuing theory, an early 1900s Dane whose specific who-goes-first challenge was the new Copenhagen telephone system, which required callers, disembodied but queued nonetheless, to be moved along in a way both maximally efficient and acceptable to all. I learned some of the ways a crush of traffic is and is not like a crush of opera fans outside Lincoln Center — the speed factor, the isolating qualities of an auto’s steel bubble, the coarsening effect of no-eye-contact anonymity. I learned that Officer Sam Morgan, of the California Highway Patrol, occasionally uses the term “cranial-rectal inversion” when referring to drivers of especially poor judgment, which was one of the most satisfactory things I learned all summer, come to think of it. I asked each professional the same questions:

1. If you were inside your personal vehicle, approaching a bottleneck that offered you the options of lineup or sidezoom, which option would you select?

2. For practical purposes — maximum vehicle flow, minimal hang-up — who’s right?

A University of Washington engineer named Bill Beaty, who was one of the first traffic scholars I located, has come up with his own bottleneck-behavior labels: Cheaters and Vigilantes. He disapproves of both. When I acknowledged belonging to the choleric wing of the vigilante order, he was unyielding but sympathetic. “That’s just human,” he said. Beaty is a proponent of the third-way prescription, which I’ll get to in a minute; he’s an electrical engineer, not formally trained in traffic flow but so interested in it that for a decade he has kept up a link-filled Web page, amasci.com/amateur/traffic/links.html, connecting to scores of diagrams and scholarly papers and discussion groups, a whole subuniverse of people preoccupied with the physics and psychology of traffic. (You can click from Beaty’s page to a comic Italian animated traffic short, a German traffic-flow simulator that twitches and rotates and a live-cam shot of one nasty section of Seattle’s I-5.)

It wasn’t until I’d spent weeks wandering this subuniverse that Tom Vanderbilt and I stumbled upon each other, like tourists buried in the same obscure travel guide, and started comparing notes. Vanderbilt is a journalist in Brooklyn who got worked up over an East Coast version of the Caldecott Tunnel Problem a few years ago, after negotiating a freeway bottleneck one day in what he described to me as a “very ‘Sopranos’ ” stretch of urban New Jersey. A lineupper by disposition, Vanderbilt unaccountably switched modes, joined the sidezoomers and cut in late. Then he worried and ruminated about what he had done. The book he ended up writing just came out: “Traffic: Why We Drive the Way We Do (and What It Says About Us).”

Vanderbilt’s book is terrific. He writes about the traffic law Julius Caesar imposed to manage chariot jams. He deconstructs “injunctive norms” (what the law tells us to do) versus “descriptive norms” (what the behavior of those around us tells us to do). He has a chapter called “Why Ants Don’t Get Into Traffic Jams (and Humans Do),” which was particularly interesting to read; it seems there’s an ant species, the New World army ant, that organizes its perfectly flowing commute processions along principles similar to those Beaty and my traffic experts invoked as they explained why the Caldecott backup is not entirely, and I say this with some reluctance, the sidezoomers’ fault.

The experts drew schematics in my notebook for me. They asked me to envision rice pouring smoothly through a kitchen funnel. They pointed out, as a Virginia Tech computer-science professor named Chris Barrett put it, that “if you move over too soon, you have this big empty piece of real estate, which could absorb that many more cars.” And I would say, yes, but they still all have to squish into the same two-lane tunnel, right? And the experts would say yes, but what really botches the flow is the stop-and-go part — which is accentuated both by the guy hanging around up there trying to last-minute jam his way in and by the hostile party in the Subaru who won’t let him, thus prompting him to try again in front of the next car, whose driver brakes while deciding whether to go into high-, medium- or low-level snit, and so on. Nearly every time I asked one of the traffic people to assume the role of the great vehicle arranger in the sky, remote-controlling each of us bottleneck drivers as if we were so many video-game characters, the reply went as follows:

FIRST, EVERYBODY REMAINS UNRUFFLED, without abrupt changes of lane or speed, as the lane-drop comes into view. Everybody takes three deep, cleansing breaths — all right, the experts didn’t say that, but they meant to — and considers both the imminent needs of everybody else and the system as a smoothly functioning whole.

Then everybody begins to slow, not too much, all in concert. All cars remain in their lanes, using all the real estate. (On the question of frontage roads and exit-only lanes, the experts waffled; those are arguably part of the real estate, they agreed, but they are meant for a different purpose, and this scenario relies upon everybody buying into the same rules. So no frontage-roading or fake-exit-laning, unless there’s a sign specifically instructing otherwise.) People in the narrowing left lanes refrain from shooting ahead, while people in the right through lanes — this is hard to swallow, for those of us inclined toward vigilantism, but crucial — leave big spaces in front of their cars for the merging that is about to commence. We resist the freeze-out-the-sidezoomer urge. We prepare to invite them in.

Finally, at clearly marked or somehow mutually agreed upon places, everybody starts conducting beautiful “zipper merges.” That’s the technical term — one-two, one-two or one-two-three, one-two-three — as indicated by the roadway configuration. The process has now worked at its ideal efficiency/equitability ratio: if all have behaved correctly, the tunnel passage has been both benign and, relatively speaking, quick. Personal sacrifice has been called for, to be sure. The former sidezoomers have sacrificed the pleasure of high-speed bypass, also known as I Beat Out the Stupid Sheep Just Now, Ha Ha (less truculent rendition: I Want to Get Home More Than I Care About Strangers Whose Faces I Can’t Even See). The former lineuppers have sacrificed the pleasure of self-congratulatory umbrage, also known as Hmph, Good Thing Society Has People Like Me. Together we have all ascended to the traffic decorum of the army ants, who as Vanderbilt observes are among the earth’s most accomplished commuters, managing to get from one place to another in large groups without cutting each other off, deciding their time is more valuable than everybody else’s, or — apparently this is the fast-lane domination method for certain traveling land crickets — eating anybody who gets in the way.

ONE AFTERNOON A FEW WEEKS AGO, Sam Morgan took me out to the Caldecott in his California Highway Patrol black-and-white, a big sedan that Morgan pulled to the shoulder so we could watch the lineupper-sidezoomer minuet from a neutral vantage point. I figured it would take a seriously dumb person to do something offensive with Morgan sitting right there, but lo, here came the exit-only-lane zoomers, gunning it past the lineup and then cutting in. Red Dodge pickup. Black Camaro. Blue Prius — great, Mr. Environmentally Superior, you have the personal-sacrifice thing down big time — white Toyota. Morgan watched them, alert but calm. “No violation here,” he said.

Morgan resembles John Wayne, except African-American and in a CHP uniform. Every time I tried to prod him into moral pronouncements about fairness, he assumed a serene Buddha face and reminded me that his job was to enforce the law. It is legal to use the exit-only lane for sidezooming — in California, at least — as long you do your cut-in before the lane line turns solid (meaning no more lane-changing permitted) near the end. It is legal to frontage-road sidezoom, as long as you observe the stop sign along the way. It is legal to be a full-on lineupper vigilante, for that matter, since you are “established” and therefore have priority in your lane, as long as your refusal to let a sidezoomer in doesn’t rise to the level of unlawfully unsafe driving. “It’s not a matter of fairness or unfairness,” Morgan said. “It’s a matter of there’s no violation, no one is being injured. Ergo, chill out. Enjoy life. You’re spending too much energy pounding the dashboard.”

Morgan gave me the Buddha look, crinkled the corners of his eyes in amusement and drove us to the operations building above the Caldecott. In civilian life, he said, he’s primarily a lineupper, just because he knows this will occasion the least vitriol. As a rule, he lets all sidezoomers in. “When I’m plainclothes, people cut me off all the time,” he said. “My thought is, If you knew who I am, you probably wouldn’t do that.”

Well, exactly. No disrespect toward Morgan, but if you’ve spent your working life being a big-shouldered guy in a patrol car, you have maybe transcended the tendency many of us have toward driving around in a state of constant micronegotiation with the world, which is so unfathomable in most respects, so beyond our field of vision and our ability to do anything about it, although not by God along the asphalt beneath our wheels. The first time I deliberately made special invite room for a sidezoomer this summer — a lane-drop bottleneck en route to Lake Tahoe, me dubiously opening the extra-long space in front of my car — I swear I could see the zoomer beside me start to accelerate, hesitate and then with me murmuring, Come on pal, we can do this together, finally shrug his S.U.V. into the merge. Neither of us had to brake. I’ll be honest, though: I missed my minuscule occasion of power, and I’m guessing he did, too, both of us having recently paid $4.69 per gallon even assuming he uses regular. “In the overall scheme of things, it’s a very short amount of time,” Morgan remarked as we got out of the black-and-white, and I followed him up some stairs to the monitor room, where two operations workers were gazing at multiple screen images of the Caldecott.

We all stood there, watching sidezoomers cut in one after another at the top of the line. One worker, Anthony Padilla, said, “That’s what I do.”

The other worker, Tim Miller, swung his head around fast. “I get in line,” he said.

I asked Padilla to elaborate — to present his case to Miller and me, as if he were chatting with us right after we’d all made it through the tunnel. “Um, I’m an aggressive driver,” Padilla said. “I would say. . . . ” He stopped and smiled. He didn’t look even a little bit apologetic. He looked, in fact, like a fisherman holding up a big shining catch. “I would say, ‘Well, the lane was open — and I took it.’ ”

Padilla and Miller studied each other. Then Miller turned to Morgan, who was contemplating them both impassively, his hands folded before him. “But I don’t have to let him in, do I?” Miller asked.

“Nope,” Morgan said. “You don’t.”

Cynthia Gorney teaches at the Graduate School of Journalism at the University of California, Berkeley. Her most recent article for the magazine was about Spanish-Language advertising.

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This entry was posted on Sunday, August 3rd, 2008 at 8:04 am and is filed under Congestion, Traffic Psychology, Traffic Wonkery, Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

9 Responses to “The Caldecott Tunnel Problem”

  1. Brad Templeton Says:

    I find a contradiction between the zipper thesis (which I suspect is the correct “fastest algorithm”) and the “wasted capacity” thesis which suggests that leaving the vanishing lane well before the join-point “wastes usable real estate.”

    In a road system like this, all that matters is the capacity of the system, in cars per hour, of the point with the slowest capacity, known as the chokepoint or bottleneck. The capacity and width of the road before and after this chokepoint is not relevant. One can have 100 lanes coming in or out, but the only way they matter is how they affect the chokepoint.

    It’s been my understanding that since “stop and go” traffic has half the cars/hour/lane capacity of modestly moving traffic, and faster traffic has even more, avoiding a stop and go collapse is the best strategy. Of course, if more cars are coming in than can get through the chokepoint, you can’t avoid that. In that circumstance, the excess capacity argument may make sense. You can’t stay long in that circumstance or you get an immensely long jam that backs up for miles, of course.

    It is the intermediate state, where we do have enough capacity (with thicker traffic) but some collapse has taken us to stop and go. Once we collapse to stop and go we must wait for a lull in incoming traffic to get out of stop and go.

    There is an argument that sidezoomers make a collapse to stop-and-go more likely. A line of cars in the continuing lane moving at a modest pace will have to stop when a sidezoomer pushes their way into that traffic. And thus the collapse starts, and maintains if traffic is thick.

    So is it possible we have two different states for a merge, one in which use of all lanes improves total flow, and another in which it hastens collapse?

    I liken this to metering lights. Metering lights are there to avoid collapse. While in the line for the metering lights, you want on the road, damnit. But you could be the very additional car which collapses the traffic to stop-and-go, making your own trip slower, along with everybody else’s.

  2. Balraj Gill Says:

    I think a major help on the approachs to this tunnel would be 2 signs on a road near to where I live in the UK. On this road, which leaves a mid-sized town, 2 lanes merge into 1. The first sign, which appears whilst the road is still 2 lanes, says “Use Both Lanes”. The second sign, which appears just before one of the lanes disappears, says “Merge in Turn”, and underneath has a diagram of the 2 lanes with 2 arrows over each other, like a zip pattern.

    Before, these signs, most drivers would queue up in the through lane and would do their best to block any drivers in the lane that was about to disappear. People (especially in England!) need to be taught that queuing up in 1 lane is not the best policy for traffic flow, when another lane is still available.

  3. Ed Baker Says:

    Pet peeve department:
    Tom, you mention in this post something that you did not, unfortunately, bring up in your wonderful book: “I think something similar may underlie the left-lane-is-for-faster-traffic dynamic on U.S. roads: It’s a good idea in practice, but someone’s always going to want to go faster, and that person’s rights are going to mash up against the guy who’s already going pretty damn fast, is exiting on the left soon anyway, and thinks he also has a right to be in the lane he’s in.”

    But isn’t the left lane not for “faster” traffic, but for “passing” traffic? How efficient is it that a two-mile line of cars be held up for 15 minutes by someone who thinks he’s got the right to drive one mile an hour faster than the five tractor trailers he’s driving next to? Sheesh.

  4. Mark Hunter Says:

    The key to the article, for me, was the idea of allowing room between cars for the zipper to work smoothly. The “idea,” I say, because this will never happen. Drivers will always want to nestle up to the car in ahead of them rather than leave room for cars to merge in front of them.

  5. Rick Mitchell Says:

    As a retired traffic engineer, here is an unavoidable fact of life: Only so many people can pass a certain point (i.e., be in the same place) within a certain amount of time, regardless of how polite they may be. This is demonstrated on freeways every day where there is no discernible conflict or disruption, other than the normal flow of traffic. The slowdown of traffic will occur whether there is a reduction in the number of lanes or not — given an increase in traffic beyond the physical capacity of the roadway, But it is most noticeable where a reduction in the number of lanes occurs. The three or four lanes that reduce to only two will have a higher capacity and must suffer some delay as the two-lane section discharges its continuing overload of traffic at the rate its own capacity can handle. The two-lane section, once you’re in it, moves, but the lanes feeding into it are disrupted — with the “liner-uppers” on the right, usually, and the “side-zoomers” on the left. If all of those drivers stayed in their lanes (as suggested by Ms. Gorney) they could merge comfortably as long as their combined flow rate did not exceed that of the capacity of the two-lane section (more or less) they were feeding into. With the four-to-two lane reduction at the Caldecott Tunnel, that would work (and indeed it does) when the four-lane section is running at about half of its capacity — approximately equal to the capacity of the two-lane section — or less than that.

    Having said that, I would agree with Ms. Gorney that having everybody stay in their own lanes would be a good idea, since it would have the effect of averaging out the necessary waiting time for all drivers in all lanes, whatever the rate of flow. Much like the operation of lanes at a supermarket, where the length of the lines at all open check stands tends to equalize (and no one feels “cheated” if another shopper joins a shorter line). Drivers in California (the ones who have been here for a few years, anyway) have learned to merge in turn — to the amazement of friends from back east, especially from Texas. However, I noticed recently while driving in Dallas and in New York that drivers in those states are also merging better as freeways (or “expressways”) become more congested.

    As she and Tom Vanderbilt have noted (along with many of us traffic engineers, believe it or not) traffic is “behavior” and humans do have an uncanny way of adapting theirs when it turns out to be advantageous. The supermarkets have also learned that keeping lines reasonably short is advantageous. I was in a line at a museum cafeteria recently where there were only two cashiers, and sure enough, congestion/delay! Supermarkets call additional checkers in at rush time and build an adequate number of checkout lines. The same things work with traffic — the building just takes longer and costs a very large amount. Sorry to break the news! Meanwhile, yes we could spread the misery evenly by using all the lanes approaching a bottleneck point. I guess the one person in a hundred with a bona-fide emergency can try to sneak by on the shoulder.

    – Rick Mitchell

  6. Ken Says:

    I’ve often thougth that a “merge zone” should be marked with both cross hatching on the pavement and signs indicating the start and end of the merge zone. This would let people know where they should be zippering together. (something along the lines of what the Brits are doing per Balraj’s comment) The vehicle whose front bumper is further forward should have right of way (rather than the person established in the lane). This would help to optimize the flow, and hopefully calm the vigilantes down by clearly indicating that “side zooming” is acceptable and proper; and give the message that 50% of the traffic should “side zoom”.

    Ken

  7. stine Says:

    Either we haven’t discussed, or it was edited out of this version, the fact that when we are taught to drive (or at least we were during the ’80s and before), we are told to leave space between vehicles. This contributes to efficiency of ‘zipper-merging’, whereas the way people (at least in Atlanta) drive is to stay 1 foot off of the bumper of the car ahead, which makes ‘zipper-merging’ impossible…..

    The real problem is that it is much to easy to get a drivers license.

  8. Bill Beaty Says:

    Note that the “side zooming” is impossible when drivers behave as suggested in the article.

    The jam is created when the majority queues up early, not using the extra lane, then “side zoomers” use that lane and create a jam as they force their way in at the last second.

    If their habit instead was to fill all lanes, then there is no long empty lane, and there are no “side zoomers.” Instead all lanes flow at about the same speed (and if one lane speeds up, then drivers will change lanes to fill it and slow it again.)

    Those commuters seem to have no trouble zipper-merging at an early point. If all lanes were filled, including the “extra” ones, why would they have trouble merging farther downstream? I don’t think they would. The trouble appears because a few fast drivers are seen as “cheating,” while the same lane filled with many slow drivers is “fair.”

  9. Anthony Mark Morningstar Says:

    The question of merging goes back to the fundamental rule of driving: Have as little interference with the other vehicles.

    The math says that with merging, there are one of two options. First, all vehicles increase spead, keeping the flow rate constant at the bottleneck. But, since most forced merging is the result of construction, and there are speed limits for construction zones, that leaves the second: That all vehicles reduce speed.

    Theoretically, if two lanes are merging, the total speed of the through lane is about one-half of the original speed. So, if BOTH lanes start reducing their speeds so that the spacing increases so that the merging lane can easily merge altenately (like the teeth of a zipper) then the flow should be maintained.

    So, if a stretch of road is at 65MPH, and merges from two lanes to one, if the vehicles reduce speed to 30MPH, this should allow all vehicles to merge easily. All vehicles will be at 30MPH. However, if someone runs to the very end and tries to merge then, he might maintain 30MPH, but force those behind him to slow down to create a hole. His gain punishes the others.

    And, if three lanes merge to one, the average speed should be around 20MPH. Simple mathematics. Again, the rude driver can cut out some amout of waiting, but will have an impact on the vehicles behind the merge.

    It is just like a parking lot. If you let one car per row turn in to the main exit, everyone will progress. The person in the last space will still be last, but that is how it should work.

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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.

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For publicity inquiries, please contact Kate Runde at Vintage: krunde@randomhouse.com.

For editorial inquiries, please contact Zoe Pagnamenta at The Zoe Pagnamenta Agency: zoe@zpagency.com.

For speaking engagement inquiries, please contact
Kim Thornton at the Random House Speakers Bureau: rhspeakers@randomhouse.com.

Order Traffic from:

Amazon | B&N | Borders
Random House | Powell’s

[del.icio.us] [Digg] [Facebook] [Google] [MySpace] [Slashdot] [StumbleUpon] [Yahoo!]
U.S. Paperback UK Paperback
Traffic UK
Drive-on-the-left types can order the book from Amazon.co.uk.

For UK publicity enquiries please contact Rosie Glaisher at Penguin.

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
Toronto

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
BoingBoing.com “Ingenuity” Conference
San Francisco, CA

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

 

 

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