CONTACTTRAFFICABOUT TOM VANDERBILTOTHER WRITING CONTACT ABOUT THE BOOK

We’re All Traffic Experts Now

At the CTS conference yesterday at the University of Minnesota, I was chatting with a traffic engineer who relayed an interesting anecdote. As a traffic engineer, he is used to addressing packed rooms of people, all filled with firmly held convictions on the way things should be done. He was chatting with a colleague, a civil engineer, about whether people ever offered any input at meetings concerning things like sewer systems. The answer was no.

It should be said that I’m of the opinion that, particularly in some local jurisdictions, community residents might actually have a better idea of how to control their streets than engineers working with standardized approaches; and that, too often, streets are merely viewed as sewers of a sort, channels for simply moving as much stuff — i.e., cars — as possible, with insufficient thought for other considerations.

But the engineer also had a quite valid point, which beleaguered traffic engineers face every day at town meetings across America when trying to, say, tout the benefits of a roundabout. Suddenly, there will be a volley of criticism: Those things are dangerous, they will make traffic worse, etc., despite all statistical evidence to the contrary. Of course, people offering these opinions typically never have actual evidence, nor have they studied the problem in depth, and yet they feel comfortable to make diagnoses on engineering problems which it seems they would not feel comfortable doing in any other arena.

I thought of this morning when reading a dispatch on how Kansas City is going to introduce ramp metering to its highways (thanks Bryan).

This, not surprisingly, prompted a letter in the local paper:

Metering entrance ramps to I-435 is a terrible idea (5/13, National/Local, “Engineers turn to ramp meters to ease gridlock”). I travel to Milwaukee several times a year, and they have metered ramps onto I-94. They slow traffic down, especially during rush hour.

The meters back cars up off the ramp onto the streets, which have intersections with stoplights, and no one can go anyplace. Half the time there is plenty of room for cars to merge in on the interstate, but because of the meter you have to stop and wait.

People who live in Milwaukee and drive on the interstates hate them. Each time I drive up there I can’t wait to get back to Kansas City, where we know how to let people get around.

Ramp meters, as I mention in Traffic, are a particular case where the individual windshield perspective of drivers cannot account for the larger flow of the traffic system, with its multitude of variables; user optimality trumps system optimality in the mind of the driver. As one engineer told me, people ask me, why are you stopping me, the highway’s moving? The highway’s moving because we’re stopping you.” But hold on, K.C. engineers, throw out those models, rip up those studies — we’ve got a driver who “travels several times a year to Milwaukee,” where “everybody” hates ramp meters (everybody, except, presumably the people who are moving more smoothly than they would be without them). But there is “room” on the highway for people to enter, this driver notes. “Room,” or “capacity” as engineers might more properly say, is, alas, not the only variable to consider in highway flow, and indeed, squeezing another driver into that “room” might disrupt the flow, pushing the stream past its critical density, plunging the system from a congested synchronous flow into stop-and-go congestion. Of course, some ramp metering schemes do send traffic back up the ramps — but one might also note that those ramps might typically be backed up already, and that in some cases this is actually made worse without ramp meters. And I need hardly point out that one cannot judge the success or failure of a ramp metering scheme simply by judging one on-ramp at any one time — rush-hour traffic on a congested urban system is an incredibly complex array of networks and flows that are well beyond the ability of any one driver to fully intuit what is going on.

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This entry was posted on Wednesday, May 20th, 2009 at 9:53 am and is filed under Drivers, Roads, Traffic Engineering, 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.

4 Responses to “We’re All Traffic Experts Now”

  1. Yokota Fritz Says:

    another example of a limited perspective occurs in meetings calling for neighborhood traffic calming. You might calm or limit that traffic on _your_ street, but all of the neighboring streets now have that traffic. You’ve just moved the problem over to an adjacent street and have possibly made it worse for the entire system.

    Several people living along the propose high speed rail route along the San Francisco Peninsula also have this limited perspective. They don’t see that HSR won’t really increase the movement of people (much) while decreasing traffic on neighboring I-280, Highway 101, local arterials and the airports.

  2. Bossi Says:

    Once again, I’m inclined to agree with you 100%. Even after having learned all about the mathematics behind ramp metering, I’m still amazed to read report after report at how well it can work. Of course, one of the primary concerns with it is the capacity for ramps to handle longer queues — an element that must be considered with any such study. However, another issue that’s been raised (and one I partly agree with as a citizen, myself) is that ramp metering “punishes” motorists living nearer to their destinations (those closer to a CBD) and “rewards” those living further away (the more far-flung sprawl). Is that something we — engineers, planners, and the general public — want to encourage? That’s to each his own.

    I can also testify as to the eagerness with which the citizenry will offer their own suggestions, which is not inherently bad except when the citizen is blind to any other considerations. Just as anyone who’s familiar with project management knows that someone’s pet project is almost always doomed to failure, such “pet ideas” are often ill-conceived and reflect only a singular viewpoint. I tend to consider citizens to be our eyes and ears of the roadway, being more than capable to at least spot when/where something’s not working out. It doesn’t take an experienced utility engineer to spot that a sewer line is backing up. While they may not know what exactly is wrong, I take in citizen’s concerns as an indication that something isn’t right.

    This could be equated to someone visiting their doctor: the patient can recognise that they have symptoms (that’s what brought them there in the first place) and they may even have a couple ideas to what it may be. Just as a doctor provides a more accurate diagnoses that pinpoints the issues at hand, an engineer takes the citizen’s reported symptoms & identifies the real issue at hand. Similarly, just as you don’t tackle a serious disease with off the shelf medication, engineers are well aware that targeting the root cause of the problem is far more effective than merely addressing the symptoms.

  3. DavidM Says:

    Here in Los Angeles ramp metering does seem to do its job well and a broken one at rush hour will result in a completely messed up right lane. However, one feature that would improve them is if their default was to green instead of to red. Once a car passes through and trips the sensor, it would then begin metering following cars. This would eliminate the need to stop when you are the only car on the ramp and prevent the wasted time, gas, and wear on the car of an uneeded stop and hard acceleration. They would continue to meter until there is no passing cars for a minute or so and then revert to green for the next comer.

  4. Grant Johnson, PE, PTOE Says:

    “It should be said that I’m of the opinion that, particularly in some local jurisdictions, community residents might actually have a better idea of how to control their streets than engineers working with standardized approaches; and that, too often, streets are merely viewed as sewers of a sort”

    You seem to be of the opinion then, that higher learning on this subject is irrelevant, and the opinions of people who have put no thought into the need for standardization should be put on par with those who have studied it and figured a lot of things out. The anecdotal accounts of typical drivers counts, for sure, but like you said, it can go both ways to criticize good traffic engineering with their personal bad experience, and it can also tout ideas that have little desired effect. Like the accidents that still happen no matter how much traffic calming is installed. Teenage boys speed for fun, and teenage girls take their eyes off the road. How’s that for biased anecdotals?

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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 Slate.com Transport column to me at: info@howwedrive.com.

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