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July 3, 2014 9:35 AM   Subscribe

Building Bigger Roads Actually Makes Traffic Worse

The Fundamental Law of Road Congestion: Evidence from US cities
We investigate the relationship between interstate highways and highway vehicle kilometers traveled (VKT) in US cities. We find that VKT increases proportionately to highways and identify three important sources for this extra VKT: an increase in driving by current residents; an increase in transportation intensive production activity; and an inflow of new residents. The provision of public transportation has no impact on VKT. We also estimate the aggregate city level demand for VKT and find it to be very elastic. We conclude that an increased provision of roads or public transit is unlikely to relieve congestion.
Generated Traffic and Induced Travel - Implications for Transport Planning (PDF)
Induced Demand And Rebound Effects In Road Transport (PDF):
Results show that congestion affects the demand for driving negatively, as expected, and more strongly when incomes are higher. We decompose induced demand into effects from increasing overall accessibility of destinations and those from increasing urban capacity, finding the two elasticities close in magnitude and totaling about 0.16, somewhat smaller than most previous estimates. We confirm previous findings that the magnitude of the rebound effect decreases with income and increases with fuel cost, and find also that it increases with the level of congestion.
The idea of 'induced demand' is that more of something will mean that more gets used. Induced Demand (PDF) :
To an economist, this is an example of demand elasticity. Simply recognizing that travel demand is elastic, however, is not sufficient to reconcile the conflicting views of engineers, planners, and environmentalists. On one side are those who argue that transportation facilities are provided to serve land uses and support economic activity; on the other are those who claim that whatever capacity is provided soon fills up to the
same level of congestion, gaining nothing. The truth can be better understood by defining induced demand in a way that uses the concept of elasticity.

More Highways, Less Congestion draws on Road Supply And Traffic In Californian Urban Areas (PDF) and Revisiting the notion of induced traffic through a matched-pairs study to argue against the idea of induced demand.
Right-Wing Media Ignore The Facts To Bash Mass Transit

Traffic Studies Systematically Overstate Benefits of Road Projects
posted by the man of twists and turns (59 comments total) 40 users marked this as a favorite

 
But the insider design-build firms that get all of those road-building contracts get lots of sweet, sweet cash.

Job creation and economic stimulus corporate capture is behind virtually brain-dead budgetary consideration being made today.
posted by mondo dentro at 9:38 AM on July 3 [2 favorites]


Anybody that lived in Atlanta through the 90s could have told you this. They doubled the size of I-75. It was congested within a week.
posted by COD at 9:41 AM on July 3 [5 favorites]


I have some city councilors who need to read this.
posted by nubs at 9:44 AM on July 3


I suspect Toronto too.
posted by maryr at 9:44 AM on July 3 [5 favorites]


Building Bigger Roads Actually Makes Traffic Worse

posted by the man of twists and turns


Eponysomething.
posted by zeptoweasel at 9:47 AM on July 3 [5 favorites]


You aren't IN traffic, you ARE traffic.
posted by humboldt32 at 9:47 AM on July 3 [43 favorites]



Anybody that lived in Atlanta through the 90s could have told you this. They doubled the size of I-75. It was congested within a week.


The thing is, induced demand has been a commonplace of urban geography courses since the nineties, if not before - I remember reading a case study on Atlanta in 1998 or so, and I'd already encountered the idea somewhere else before, IIRC.

It's one of those politically unpalatable truths that is always having to be rediscovered since it's ignored or buried the minute it's brought up.
posted by Frowner at 9:54 AM on July 3 [8 favorites]


The most optimal configuration of a city in the original Sim-City is mixed use light commercial and residential connected by light rail and 0 roads.
posted by Skwirl at 10:00 AM on July 3 [5 favorites]


This becomes pretty obvious when you view highways as a subsidy for living further away. People take advantage of that subsidy until such time as equilibrium - meaning, traffic congestion back at the old levels - is achieved.
posted by mhoye at 10:05 AM on July 3 [12 favorites]


Induced demand, the filthiest little secret hogtied and ballgagged in the closets of traffic engineers everywhere.
posted by entropicamericana at 10:06 AM on July 3


humboldt32: You aren't IN traffic, you ARE traffic.

This was recently said to me, and it was (sadly) an eye-opening moment, totally a Keanu Reeves "whoa" event.
posted by filthy light thief at 10:08 AM on July 3 [6 favorites]


I was going to say, have any of these people ever played SimCity? (Now granted, it reflects the biases of its designers, but you quickly learn that building more roads is never the solution. Also, Godzilla is a great tool for urban renewal.)
posted by fifteen schnitzengruben is my limit at 10:08 AM on July 3 [6 favorites]


No, everyone else is traffic! They are also driving at the wrong speeds! And not using their blinker then forgetting to turn it off.

I am a flawless driver. Dad lets me drive slow in the driveway.
posted by maryr at 10:11 AM on July 3 [8 favorites]


But the insider design-build firms that get all of those road-building contracts get lots of sweet, sweet cash.

I'm not a transportation person, but I was under the impression that design/build was actually a small percentage of highway contracting. Am I incorrect? Design/build is theoretically faster and more efficient, but you have to build in qa/qc and cost control very carefully.
posted by Dip Flash at 10:15 AM on July 3


I walk. The rest of you are traffic.
posted by pracowity at 10:21 AM on July 3 [10 favorites]


Design-Build and Public Private Partnerships are becoming more significant infrastructure delivery methods due to the perception that you get more road for fewer public dollars. Whether that's true or not, I'm not convinced.

More roads aren't always a great solution, but roadway construction is just about the best job creation task there is. I'm biased , naturally, being on the design side. But construction makes available very well paying union gigs.
posted by hwyengr at 10:21 AM on July 3


Did not RTFA, but anybody that's ever played Sim City knows this.
posted by bashos_frog at 10:25 AM on July 3


This has some other names that I didn't see listed in the title. In game theoretic analysis of networks, a version of this kind of paradox is called Braess's paradox.

en.m.wikipedia.org/wiki/Braess%27s_paradox

"t adding extra capacity to a network when the moving entities selfishly choose their route, can in some cases reduce overall performance. This is because the Nash equilibrium of such a system is not necessarily optimal."

Its one of many versions of the prisoners dilemma only here it is laid on top of a network environment. I haven't seen this presented in terms of increasing the capacity of a route before (but I have not read broadly in the transportation or networks area) but the results are known for cases when you add new routes to a network.

I'm drawing a blank on this but I remember there being an upper bound on just how large the decay can reach. Its both the increase in driving time that occured in Nash equilibrium that makes it interesting but also that there is an upper bound on just how bad that Nash equilibrium can be. It'll come to me later.
posted by scunning at 10:27 AM on July 3 [1 favorite]


We've seen this in Charlotte, NC with I-485 outer belt. A professor at UNC Charlotte wrote in the 1990s more than once in the indie paper Creative Loafing that the outer belt would create more traffic and it has. Portions of the outer belt have been widened and the entire project isn't even finished yet.
posted by zzazazz at 10:28 AM on July 3 [1 favorite]


OTOH, better designed roads certainly can help. Various parts of the 405 updates in LA, particularly the entrance/exit redesigns, have reduced surface congestion around the freeway quite noticeably.
posted by flaterik at 10:32 AM on July 3


Was up in DC and the Northern VA area earlier this week, and was thinking much the same thing. Only a developer could look at this area and think that the solution was more tarmac.
posted by idb at 10:35 AM on July 3


While congestion may not improve, the total utility could still increase. I'm not persuaded that more roadways aren't worthwhile investments.
posted by jewzilla at 10:37 AM on July 3 [3 favorites]


I walk. The rest of you are traffic.

Nope, you're still traffic. You are walking too slow, or you are stopping in the middle of the goddamn sidewalk to look at something (like your phone), or you and your friends are taking up all the room while you wait for a table at the restaurant.

Basically, no matter the mode of transport, all of you annoy me!
posted by rtha at 10:40 AM on July 3 [3 favorites]


I've lived in the same place now for more than 15 years, a northern suburb of Seattle that has about a 40 minute commute to downtown and about a 20 minute commute to Redmond in the absence of traffic. Traffic can double the former and triple the latter, to the point where it only takes 10 minutes longer for my husband to bike from our house to his job in Redmond than it does to drive. In that time, they've done a LOT of things to try and mitigate traffic along 405, including adding new lanes. But the thing that helped the most was adding an HOV-only left-hand entrance/exit ramp and bus stop at the big hospital. That has cut 10 to 15 minutes off the drive from 520 to 522 at rush hour. In conclusion: traffic management is hard and counterintuitive.
posted by KathrynT at 10:47 AM on July 3


I always hear this, but my guess is that these people don't live in Los Angeles/SoCal

Over the last decade plus of improvements, the 405 between the 101 and LAX is much much better. The 5/14 interchange improvements that have been going on for the last 4ish years have brought astounding improvements. The 5 and 405 improvements in Northern Orange County (don't get to South County much) have also made 100's of thousands of people's lives much better.

So yeah, I guess in another 20 years we might be in the same traffic. Until then, the 150,000+ people who drive over the Sepulveda pass twice a day will have extra hour per day effectively added to their day.
posted by sideshow at 10:52 AM on July 3 [1 favorite]


Basically, no matter the mode of transport, all of you annoy me!

It's true. Escalators, airplanes, subways, buses, bicycles, trolleys, shopping carts... I can think of complaints for all of them. I guess I don't have any elevator specif-- nope, people who take the elevator one floor when the stairs are right there. You're all jerks, all of you.
posted by maryr at 10:53 AM on July 3 [4 favorites]


Well that's settles that: Induced demand is a commie myth. Motor on, America!
posted by entropicamericana at 10:55 AM on July 3


So, isn't that the point? They build more roads to have more traffic. More traffic means more people living there, means more people paying taxes, means more demand for places closer to the center, means higher property taxes?

Am I missing something fundamental about this "mysterious" correlation? Is the metric they are using total miles driven or total miles driven per person or what? If it's just total miles, well, that's exactly the _point_ of building roads, isn't it?

(No, I am not arguing against induced demand existing, I'm just saying, aren't they trying to induce demand?)
posted by artichoke_enthusiast at 10:56 AM on July 3 [2 favorites]


I prefer to use the term automobile traffic.

We can use this to our advantage. These studies can hold true for other kinds of traffic as well. Create more room for cycle/ped/skates/skateboard/etc (active transportation) and we get more people using active transportation.
posted by aniola at 10:58 AM on July 3 [3 favorites]


Automobile normativity? Autonormativity? Car normative.

Car traffic, car parking.
Sidewalks: ped traffic. Benches: ped parking.
posted by aniola at 11:00 AM on July 3 [1 favorite]


Someone please tell the citizens of my fine city. We're about to spend $5 billion (combined federal, provincial, city dollars) to finish the last 1/4 of our ring freeway.

You can already drive nearly this route on older 80 km/h expressways, with something like 10 traffic lights over 30 km. The newspaper editorials call this route, with its traffic lights, a "nightmare".

$5 billion could buy us so much light rail... we already have a nice N-SE route mapped out and everything. That one route would only cost $2 billion and move 100,000 people on its opening day. And, it wouldn't skirt the edges of this beautiful place.
posted by Pruitt-Igoe at 11:11 AM on July 3 [1 favorite]


Part of the problem, and why larger highways exacerbate this, is because you can build 40 lanes of freeway but you still can't get cars off it fast enough. Some very smart cookies at Berkeley took a look at it.

I think part of the problem is this obsession with four-way intersections in the American road system. Roundabouts? Traffic circles? Nup gotta go with the four way stop there, chief. So you end up with massive queues on clogged freeway off ramps while they wait for the traffic signal to change.
posted by Talez at 11:18 AM on July 3 [1 favorite]


This has been known for quite some time; it's one of the central critiques of Robert Moses' preference for roads and bridges over expansion of mass transit in Robert Caro's The Power Broker. From the Wikipedia article about the book: "Here were these mathematical formulas about traffic density and population density and so on," [Caro] recalled, "and all of a sudden I said to myself: 'This is completely wrong. This isn't why highways get built. Highways get built because Robert Moses wants them built there. If you don't find out and explain to people where Robert Moses gets his power, then everything else you do is going to be dishonest.'"
posted by Halloween Jack at 11:20 AM on July 3 [6 favorites]


Building Bigger Roads Actually Makes Traffic Worse

Anyone who has played the latest version of Sim City knows this. Especially when the bastard in the next city has ten casinos and the traffic on the region freeway backs up into yours...
posted by DWRoelands at 11:34 AM on July 3


Anybody that lived in Atlanta through the 90s could have told you this. They doubled the size of I-75. It was congested within a week.

Atlanta: Our citywide pastime is idling.
posted by 1f2frfbf at 11:39 AM on July 3 [3 favorites]


Am I missing something fundamental about this "mysterious" correlation? Is the metric they are using total miles driven or total miles driven per person or what? If it's just total miles, well, that's exactly the _point_ of building roads, isn't it?

Part of it is simply a bit of honesty about what spending billions and trillions of dollars of public money actually is about.

I mean if freeway expansion (for instance) were honestly portrayed as "Hey, we're going to attract zillions of residents and businesses out here to the far suburbs away from the city center, and help encourage sprawl and the hollowing out of the city center in a massive way, and help encourage a whole bunch of new greenfield development out here where the new roads and freeways are instead of fixing and redevelopment the part of the metro area, and we're hoping and planning to get neighborhoods and shopping and jobs spread out all over the place so that you have to drive drive drive drive drive just to get anywhere useful and your neighborhood shopping center will now be 20 minutes by automobile away instead of a 20 minute walk, everybody pitch in and support this awesome new massive project for our region!!!!?!!!"

Instead we get a bunch of handwaving and dishonest BS about road capacity and congestion and blah-blah-blah.

Most everyone will sign on the "reduce evil congestion through a few simple and proven measures."

Hardly anyone wants to sign on to "rebuild our communities in completely dysfunctional ways through massive government subsidies."
posted by flug at 11:47 AM on July 3 [2 favorites]


Here in Fort Worth, we are testing out roundabouts on a few roads, actually! So far they're ok, though lots of people are unclear about when to wait/when to go. We also have an ancient Traffic Circle that is a death trap, like a master class in How Not to Do Roundabouts, but the new ones are actually functional.

I would still like a useful bus system though.
posted by emjaybee at 12:03 PM on July 3


How about taking 5 lanes down to 2 while adding onramps? I'm looking at you Calgary!
posted by blue_beetle at 12:05 PM on July 3 [1 favorite]


If it's just total miles, well, that's exactly the _point_ of building roads, isn't it?

To restate my point above more concisely, the point is most definitely and emphatically not to simply drive more miles.

The point is to connect people with the things they want and need.

If it takes twice as many miles driven to connect people with the things they want and need (for instance by spreading them all twice a far apart with bigger/faster roads conveniently built to fill up the space in between) then that is not some sort of accomplishment in itself - it is simply a giant waste.

There is probably going to be some collateral damage there, too, like a bunch of shitty communities filled with wide, fast 'traffic sewers' and where every possible way of getting around, other than driving in a personal automobile, has suddenly become impossible and unworkable because everything is spread out at convenient driving distance but no longer at usable biking, walking, or transit distance - but let's not even get into that issue.

Lives in Sprawl Central, U.S.A., but is not bitter, not bitter at all--no . . .
posted by flug at 12:06 PM on July 3


flug -

What I'm saying is:

total miles = people x fraction that drive x miles driven/driver.

Total miles goes up implies that one or two or all three of the factors goes up. The entire point of building roads to is to make the first factor -- the number of people -- go up. City planners want more people in their city, don't they? The other two factors (which must go up as you build more roads) will increase, but that's seen as a sort of acceptable collateral damage to the road builders, I would think.

I'm really not trying to make a case for building roads (which are awful -- I haven't commuted by car since high school) vs public transportation, I'm just curious exactly how much of this "unintended" consequence is actually the "intended" consequence -- more people!
posted by artichoke_enthusiast at 12:29 PM on July 3


Funny, this idea was totally covered by the book Traffic: Why We Drive the Way We Do (and What It Says About Us) a few years ago.

Other counter-intuitive ideas included making roads less safe (so people pay attention when driving).
posted by St. Peepsburg at 12:40 PM on July 3 [1 favorite]


flug -

Just saw your earlier, longer comment. I get your point, and I'm with you on the pointlessness of expanding freeways for the sake of "congestion" and the endless way in which these deals are sold to the public, but much like seemingly everything about modern life, they have a ruthless efficiency to them that is hard to ignore.

San Diego (my fair home) had 500K people living in the county in 1950. Now, it's 3.3 Million. Those 3.3 million people could not possibly live in the county without the extensive and expensive freeway system that exists. Now, as for why they would _want_ to live there, given that about 2.3 Million of them have horrific commutes, is beyond me but it is hard to imagine that an awesome public transportation network centered on downtown would have ever reached the level of total population that the sprawling, never-ending suburbs managed to achieve in very short time.

People have terrible commutes, they spend their lives in rolling death traps, and the freeways have destroyed the canyons of the county and its native wildlife. But the 3.3 million people are there! Somewhere, some city planner is smiling and congratulating himself on keeping those people from choosing to live in LA instead.
posted by artichoke_enthusiast at 12:51 PM on July 3


San Diego (my fair home) had 500K people living in the county in 1950. Now, it's 3.3 Million. Those 3.3 million people could not possibly live in the county without the extensive and expensive freeway system that exists.

Somebody please alert the people of New York, Europe, etc., etc., etc.
posted by entropicamericana at 1:04 PM on July 3 [7 favorites]


Those 3.3 million people could not possibly live in the county without the extensive and expensive freeway system that exists.

They designed the city around freeways and then claim the city doesn't work without freeways. It's circular logic. The best thing that every happened here in Vancouver was when we rejected plans for an urban freeway system in the 70s.
posted by no regrets, coyote at 1:38 PM on July 3 [10 favorites]


In Seoul about ten years ago, they tore down an urban freeway and transformed a big chunk of the city. Oh, and city traffic actually improved.
posted by zardoz at 1:44 PM on July 3 [1 favorite]


If seems like a huge part of the problem is that increased traffic affects people at the bottom of the economic pyramid much more than people at the top; at least where I live. I know people with lower incomes who have 1-3 hour commutes, whereas people who can afford expensive real estate get sub hour commutes and yet have a larger voice in policy.
posted by BrotherCaine at 1:44 PM on July 3


In Seoul about ten years ago, they tore down an urban freeway and transformed a big chunk of the city. Oh, and city traffic actually improved.

It also made the mayor who spearheaded it, 2MB, very popular, helping him win the presidency. Admittedly, the Seoul mayorship is seen somewhat as a stepping stone to higher national office, which isn't the case with mayorships here, but that lure of future power may be a decent enticement to politicians.
posted by qcubed at 2:12 PM on July 3 [2 favorites]


It's one of those politically unpalatable truths that is always having to be rediscovered since it's ignored or buried the minute it's brought up.

It's pretty sad that a principle that basically reassures "actually things will be measurably better for users of all modes if we choose not to spend a bunch of money on this dumb thing!" could be considered "politically unpalatable".

On the other hand, I think the problem is as much technocratic as political--

induced demand has been a commonplace of urban geography courses since the nineties, if not before

I would be very surprised if the majority of traffic engineers had taken coursework in human geography.
posted by threeants at 2:16 PM on July 3


The photo at the top of the page of a traffic jam? (Presumable L.A.) It gave me a case of the heebie-jeebies as bad as the snake den further upthread did to the herpetophobics. I've been to Los Angeles six times in the last six years…and I am finished with that place.
posted by kozad at 2:46 PM on July 3


aniola: "I prefer to use the term automobile traffic.."

I prefer to use the term "ipsomobile" because I don't like to mix my Latin and Greek roots.

Fine, fine, "autokinetikon" if you must.

Talez: "I think part of the problem is this obsession with four-way intersections in the American road system. Roundabouts? Traffic circles? Nup gotta go with the four way stop there, chief. So you end up with massive queues on clogged freeway off ramps while they wait for the traffic signal to change."

Here in Peoria (land of the pre-platted Northwest Ordinance and square, square roads!) we have been getting roundabouts at a few high-density intersections the past few years ... they've put in four just in the past two years.

They also just took one of our busiest downtown roads and our busiest downtown intersection, narrowed the whole shebang from two lanes each direction (with left turn lane) to one each direction (with left turn lane), made the intersection a "pedestrian-friendly" tulip-style intersection, and made the rest of it bike lanes and on-street parking.

Everyone was like TRAFFIC ARMAGEDDON!!!! but after about two weeks it settled down and it's pretty pleasant now, much less traffic at that intersection, more pedestrians, less concern you're going to run someone over (because the sidewalk is too close and too narrow), and it doesn't take any longer to get through the intersection than it did before. I'm curious to see how it fares when the (largely pedestrian) college students come back in the fall.

We've had a pretty vocal pedestrians-and-bikes-and-new-urbanism contingent for the last decade, who for a long time didn't win any victories (and even when they did, like some changes to the zoning code, the council just always voted special exemptions to the new urbanist parts of the zoning code), but they've been a loud voice in local development for a long time now, so when our (very new urbanist) city manager suggested a roundabout, people were like, "Oh, yeah, I've been hearing about those for a while," rather than "WHAT DEVIL'S RING IS THIS?" There was still a pretty spirited debate about it, but it was a possibility people were familiar with and it was a lot easier to persuade the city to try it.

Still too sprawl-oriented a city council, but at least we can now get urbanist projects TOO instead of nothin'-but-sprawl. Maybe another decade moves the needle to new urbanist projects being preferred.
posted by Eyebrows McGee at 2:56 PM on July 3 [6 favorites]


The photo at the top of the page of a traffic jam? (Presumable L.A.) It gave me a case of the heebie-jeebies as bad as the snake den further upthread did to the herpetophobics. I've been to Los Angeles six times in the last six years…and I am finished with that place.

Not only is that not Los Angeles, it's not the United States. Those look like Korean cars to me.
posted by sideshow at 3:18 PM on July 3


I've been to Los Angeles six times in the last six years…and I am finished with that place

I hate being traffic. I've lived in Los Angeles for 10+ years, and I'm only ever in serious traffic when I go to Dodgers games, which is about 5x a year. I live near where I work, my kids' school is walking distance, and I don't go out to dinner unless the reservation is for after 7:30. I make airline reservations for 7am. I know where and how to drive on surface streets ("the ladder"). I ride my bike often. I plan. Yes, that's a lot of work to avoid traffic and be (relatively, for here) car free, but there are so many other advantages of living in a large city with amazing weather and creative people that I am happy to spend time planning/biking/etc. to make it work.
posted by cell divide at 3:42 PM on July 3 [1 favorite]


If you build more roads, and they become congested rapidly, that is an indication that the scale of the problem is larger than you think, that there's a vast, invisible demand for transportation that's not being met. The ceiling to transportation use isn't what you observe on the road now, it's what people are willing to put up with to do the driving they need to live their lives.

I wouldn't call it "induced demand," like having roads causes driving. This is sometimes touted as an "unobvious" result, and believe me, I know all about problems having unintuitive causes. But that's not what's happening here -- having more roads doesn't magically cause traffic, rather, it removes the throttle that's always limited all the driving people need to do. Rather, a gross undersupply of transportation has always been a harsh limiting factor. That doesn't mean, as seems to be implied by this article, that you throw up your arms and say "why bother."

The capacity for traffic is a fundamental limiter. All the things we use roads for -- among them, many forms of commerce -- they all rely on the existence of roads. Increase traffic capacity and you allow that commerce to increase closer to the level it would like to be at, which is a good thing, indeed a big part of what we have roads for, enabling those uses, but that's not being considered in the Wired article, which would rather us perceive the problem as a hand-wavey counter-intuitive result (OMG EVARTHING U KNO IS RONG) without looking too hard at how it operates. (And of course, a side effect of that would be an increase in pollution, which is a big negative. I'm not arguing for or against an increase in roads personally, just trying to explain the nature of the problem.)

If you reduce the number of roads, what ultimately happens is a lot more people will be avoiding driving at all. Some will find alternatives like public transit, which is good. But others will just get frustrated and wonder why the hell they live in your city, and because those kinds of complaints are not as readily visible they tend to be ignored. And you'll also restrict transportation-using commerce, and you'll reduce the distance people are willing to live from their workplace, which will increase city core land values and rents.

Energy production and use works the same way. There is no more fundamental limiter than energy, after all, that's baked into the nature of our universe. If we found a source of plentiful, cheap energy, people would find new uses for energy and not focus on conserving it, and eventually we'd be right back at having an energy problem. That's why I've suggested, in the past, that finding a way to make nuclear fusion workable could greatly harm us, because we have lots of hydrogen in water for making into energy, but we also have lots of things we'd like to use energy for, and we'd quickly find more. Finding new energy sources is important, but conversation of resources is also important, regardless of how plentiful those resources may seem.
posted by JHarris at 4:34 PM on July 3 [3 favorites]


An interesting thing about induced demand is it isn't really a single monolithic thing, it's actually a series of interconnected decisions. Using new lanes on the freeway from A to B as an example, some of the changes that can happen (roughly in order of magnitude from most to least common) are: And these all add up into more traffic on the freeway than you might have expected if you hadn't taken them into account.



I wouldn't call it "induced demand," like having roads causes driving. This is sometimes touted as an "unobvious" result, and believe me, I know all about problems having unintuitive causes. But that's not what's happening here -- having more roads doesn't magically cause traffic, rather, it removes the throttle that's always limited all the driving people need to do. Rather, a gross undersupply of transportation has always been a harsh limiting factor. That doesn't mean, as seems to be implied by this article, that you throw up your arms and say "why bother."

I think that in theory, you're right, in that the people who are producing the additional induced traffic are getting some sort of benefit from it, whether it's that they leave closer to the time they want to or they get to bring their family with them to help pick out the couch. (I think that "need" is a strong word, and a lot of the benefits are "wants".) The problem is that there is also a series of costs associated with these benefits -- you can't look at a system, conclude that some benefit somewhere exists so it must be a good solution independent of what the cost for that benefit is. We build $100M of freeway, and some people get to sleep in 15 minutes later - while that is a benefit they experience, it may not actually be worth $100M.

If road users experienced the transportation costs directly, then the only additional traffic on the road would be that which was truly worth it. However, much of the cost of transportation is either experienced indirectly (the road may be built through a general tax bill), subsidized or not experienced at all, as externalities. In the practical real world, because of these subsidized or not-experienced costs, we are already generally travelling more than we should be, and it may not be such a bad thing that we don't spend fortunes to travel as much as we possibly can.
posted by Homeboy Trouble at 6:40 PM on July 3 [2 favorites]


Route shifts - drivers going from A to B take the freeway instead of surface streets

There's a great Stephen King short story, that I'm constantly on the fence about posting, where the narrator mentions how freeways/interstates tend to fill the mind in terms of possible routes, and the state highways, country roads, or other roads may be shorter, faster, and less congested, but stick out less in the mind while route planning.
posted by the man of twists and turns at 8:53 PM on July 3


PAVE

EVERYTHING
posted by El Sabor Asiatico at 5:55 AM on July 4


Many of these analyses seem to ignore an additional important factor - that is, the freeway is neither the origin or destination of the traffic and adding more lanes will in fact lead to more congestion at entry and exit points where traffic merges as there is necessarily some overhead in doing this (we all have finite reaction times!). I'm by no means advocating new roads, but I wonder to what extent this particular problem can be alleviated by different entry and exit freeway designs. (I had some time to ponder this on the while stuck in traffic near Swansea on the M4 today)
posted by piyushnz at 2:10 PM on July 4


The reason self driving cars are such a big deal is as follows:

A road that can handle 1500 cars/hr with humans can handle 37500 cars/hr with machines. Nothing else can help nearly as much.
posted by effugas at 8:08 PM on July 4


A road that can handle 1500 cars/hr with humans can handle 37500 cars/hr with machines. Nothing else can help nearly as much.

Which is why I'm convinced, despite talk of self driving cars enhancing urban environments, that they will usher in a new era of even more extreme (and long term) sprawl.
posted by Defenestrator at 7:54 AM on July 7 [1 favorite]


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