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The entire concept that induced demand means there's no benefit to increased capacity seems so silly to me, and it seems to skate by with little scrutiny in the

The entire concept that induced demand means there's no benefit to increased capacity seems so silly to me, and it seems to skate by with little scrutiny in the urban planning world. To analogize to technology, this is like saying "more bandwidth doesn't improve connectivity; increases in bandwidth get eaten up by more bandwidth-hungry applications". Sure, broadband connections were "eaten up" by new applications, like YouTube. But that's good! New things are possible that weren't before and users are benefiting! Similarly, if 20% more cars are traveling on a freeway now... they're choosing to do that for some reason. They're benefiting somehow, either because it's not actually as bad as before, or more people can be carried at the same speed (and they've switched away from an alternate route that was slower and reduced traffic on that route, or they're able to go somewhere at a certain time when they previously weren't, or something). No one's like "there's a new lane on the 5 and it's not moving any faster than it was before, I think I'll start taking it".

throwaheyy 4y ago
Poor analogy. More bandwidth does not occupy more physical space. Wider highways, very much so, to the point of producing an environment hostile to peaceful living, more noise and pollution, barriers to walking and nature etc.
- repsilat 4y ago
  That's a different argument. The grandparent wasn't making a general case for the net benefit of added lanes, they were addressing the narrow argument of "induced demand" somehow proving that improvements are futile. And for that purpose the analogy was pretty good.
  - throwaheyy 4y ago
    My point was that improvements ultimately are futile because there are practical limits on how wide you can make a highway.
- listenallyall 4y ago
  Highways are typically built away from residential communities. Not always, of course, but far more people live next to (or on) surface streets than freeways. People are going to drive to work. Attempts at carpooling have been utter failures. Wider highways means more capacity means more people will take them, which is actually better for noise and pollution and safety, than driving on surface streets. Idling waiting for a red light is far worse, emissions-wise, than 15-20 mph in a freeway "traffic jam". People don't expect to walk across a freeway, they do expect to be able to walk across the streets near their home, which becomes nearly impossible when traffic is so bad on the freeway that everybody starts taking the off-freeway "shortcut" or "bypass" that your kids ride their bike on.
  - theGnuMe 4y ago
    >Highways are typically built away from residential communities. lol, what?
    - listenallyall 4y ago
      What do you believe is the percentage of homes closer to a freeway than to a surface street?
  - kdmccormick 4y ago
    This may be true in rural areas or car-centric cities, but in the Northeast US and many other dense parts of the world, freeways butt up against or even plow right through neighborhoods, especially lower-income ones. Until the late 90s, an elevated freeway ran through the middle of Boston. It's bad for safety, bad for health, and bad for happiness. In those places, it makes more long-term sense to invest in transit and bike infrastructure instead of inducing more demand for urban freeway bandwidth.
    - listenallyall 4y ago
      Bicycle riders ride on surface streets. For safety reasons, they should be in favor of diverting the maximum number of vehicles, especially large trucks and commercial vehicles, towards freeways and away from surface streets. Widening highways facilitates that.
- jcims 4y ago
  My brother has spent the last 25 years adding bandwidth to the local metro area. It most certainly occupies more physical space, sometimes at tremendous expense.
  - throwaheyy 4y ago
    Ok, maybe it involves stringing up a new cable, onto poles already carrying many cables. That’s not even close to being comparable to widening highways.
silverpepsi 4y ago
Yep there should be a two dimensional metric of how many tax payers' needs were met and how well were they met. Serving more tax payers without an improved performance (time to destination) metric is still a win.
- bobthepanda 4y ago
  The cost benefit analysis is a generally accepted way of doing this. Interestingly enough, transit projects in the US are actually funded based on how competitive their CBA is, but highway projects are not and are funded via formulas defined in law by Congress.
repsilat 4y ago
I generally agree, but there are better versions of the argument. One of them is the Braess network paradox[1]. In short, under a model with simple game-theoretic assumptions about behaviour ("people find the shortcuts") and traffic/speed congestion functions an added road/connection can do more harm than good -- in the extreme case, slowing down every actor. The toy model may not actually be realistic, but I think reality might not be too different. Say the congestion delay function is smooth, and one added car doesn't change travel time much. How much does one of the new trips with the new infrastructure improve the life of the driver over the status quo? Very little: if travel times are the same, they only benefit to the extent that their trip would have slowed down traffic before. So generally you might say, - Adding the lanes but leaving behaviour the same would speed up traffic, improving global utility, - Letting traffic reach equilibrium (if speeds go back to what they were before -- big assumption) removes that benefit for existing travellers and doesn't much improve the life of new travellers, and is a net negative for global utility nearly equal in size to the earlier increase. - Maybe an argument for tolls? 1: https://en.m.wikipedia.org/wiki/Braess%27s_paradox https://en.m.wikipedia.org/wiki/Braess%27s_paradox
kurthr 4y ago
Even more than that, there are many places where there is a short narrow section of the same road (e.g. a 1 lane section connecting 2 lanes or 2 lane section connecting 3 lanes) that causes hugely inefficient usage. Fixing those is likely to be dramatically more cost/externality efficient than the alternatives. Also, those little squeezes are the very points where the Braess paradox actually shows up. Why let it?
wolpoli 4y ago
The concept of induced demand shifts the government from a role where it manages the supply of road to serve motorists, to a role where it exists to manage traffic. The critical differences in that the motorists are no longer meaningful stakeholders in the discussion, but merely as part of traffic.
- tadfisher 4y ago
  Those motorists overwhelmingly demand solutions to traffic. The folks losing their homes to freeway expansions are the ones who should have the largest stake.
  - wolpoli 4y ago
    I agree that folks losing their homes to freeway expansions have stake in this. I am pointing out that the language shaped discourse against motorists. This is not the only example either. Motorists are compared with rats in other situations [1]. [1]: https://en.wikipedia.org/wiki/Rat_running https://en.wikipedia.org/wiki/Rat_running
bobthepanda 4y ago
The issue is not that induced demand exists (it exists for nearly every kind of travel) but that the cost-benefit ratio for highways is actually rather low, because highway lanes are so low capacity and fill up fast. (A standard metro line can easily carry 30-60k persons per direction per hour; the figure for a highway lane is 2.5k.) US highway transportation funding is not generally subject to cost effectiveness analysis but distributed according to formulas to the 50 states and funded at a 90-10 federal-local ratio, which is very different from how other modes of transportation are funded. Quite frankly, it is impossible to build your way out of highway congestion, without totally gutting American metropolitan areas, because there isn't just empty land in the middle of those for new highways. Which is also the root cause of most highway opposition these days, in existing areas; but new areas are not much better, in that usually this results in playing musical chairs with regional development rather than totally new net growth.
- rayiner 4y ago
  > but that the cost-benefit ratio for highways is actually rather low, because highway lanes are so low capacity and fill up fast. (A standard metro line can easily carry 30-60k persons per direction per hour; the figure for a highway lane is 2.5k.) That’s not the complete cost benefit calculation. A 4-lane highway costs $5-10 million per mile in suburban areas. Meanwhile, the DC Metro’s recent expansion through exurban Virginia mostly along an existing right of way cost $200 million per mile: https://www.heritage.org/transportation/commentary/washingtons-new-6-billion-metro-line-needs-simpler-solutions https://www.heritage.org/transportation/commentary/washingto.... So even if the rail carries three times as many people, it costs 20 to 40 times as much money per mile. That’s the cost side. On the benefit side, few places can saturate a subway line that carries 30,000 passengers per hour. Over the Thanksgiving weekend, just 5,000 people per day used the new Silver Line stops in Virginia. Even the design estimate of the Silver Line was 30,000 per day, and actual use has been a fraction of that. So the benefit side of the equation is a lot lower than the theoretical peak.
  - bobthepanda 4y ago
    It makes more sense to compare like for like. The current project to expand I-66 in the DC suburbs of Virginia is $3.7B, which is $160M per mile along an existing right of way.
oefrha 4y ago
Instead of mindlessly deploying larger pipes to accommodate more HD video streams in MPEG-2, sometimes you design better compression in the form of AVC/HEVC.
- anticensor 4y ago
  Let me translate it into transport jargon: Instead of mindlessly deploying larger highways to accommodate more cars, sometimes you design better compression in the form of trains.
- DesiLurker 4y ago
  why not both? public transportation also need to be paired with good local connectivity (I have seen this first hand in sf bay-area). but then if local nimby's dont let local housing built and economic centers dont shift then all this means is people dont have a choice but to commute long distances (I have). I'll tell you the public transportation is definitely doable but it needs a lot more frequency and much better connectivity. definitely not the half assed way SV does it. Also time people spent doing same traveling between driving vs Public transportation needs to be comparable as in maybe 50% more not 2x or 3x (though that would be covered by my higher frequency & better connectivity comment but it needs to be a design consideration).
deleted 4y ago
[deleted]
stephen_g 4y ago
Obviously it's not a hard truth that no capacity improvement is worth it, but the idea of induced demand is describing something that is quantifiably true in many cases. And it's all about cost and physical space - that's why nobody worries much about induced demand in, say, bike lanes or train lines, because the route capacity of those modes is so much higher than car lanes. The issue at the end of the day is that, assuming a certain population density and a growing population, roads tend to become extremely expensive (because of the required property buybacks, etc.) while at the same time cars fundamentally take up too much space in urban/suburban areas for the number of people they tend to carry. (Obviously this is almost never an issue in rural areas, given the low population density). So it's not so much the issue that you couldn't theoretically build enough capacity, it's for most brownfield areas, you won't add enough capacity to fix traffic because of the huge cost - not to mention environmental destruction, or knocking down people's houses to replace with more and more roads, etc.. This is of course very different to, your example of internet bandwidth, where you can trivially increase the capacity by many multiples without taking up any more space physically. The closest analog in the transport world would be rail, which uses very little real estate compared to huge potential capacity. Given that fundamental issue (the cost and space that roads take up, and the fact that cars are one of the least volumetrically efficient modes of transport), what becomes observable is the ironic fact that the cities that tend to be best to drive in are the ones that have provided many good alternatives of good public transit, bikeways, etc. as opposed to the cities that were designed around the car.
stby 4y ago
You may want to read the article then, it's full of examples to prove that the concept is not silly. > No one's like "there's a new lane on the 5 and it's not moving any faster than it was before, I think I'll start taking it". The point here is that the new lane does actually "solve" traffic immediately after it has been opened. The improved travel times create the demand and eventually this leads to more congestion.

throwaheyy 4y ago

Poor analogy. More bandwidth does not occupy more physical space. Wider highways, very much so, to the point of producing an environment hostile to peaceful living, more noise and pollution, barriers to walking and nature etc.

repsilat 4y ago
That's a different argument. The grandparent wasn't making a general case for the net benefit of added lanes, they were addressing the narrow argument of "induced demand" somehow proving that improvements are futile. And for that purpose the analogy was pretty good.
- throwaheyy 4y ago
  My point was that improvements ultimately are futile because there are practical limits on how wide you can make a highway.
listenallyall 4y ago
Highways are typically built away from residential communities. Not always, of course, but far more people live next to (or on) surface streets than freeways. People are going to drive to work. Attempts at carpooling have been utter failures. Wider highways means more capacity means more people will take them, which is actually better for noise and pollution and safety, than driving on surface streets. Idling waiting for a red light is far worse, emissions-wise, than 15-20 mph in a freeway "traffic jam". People don't expect to walk across a freeway, they do expect to be able to walk across the streets near their home, which becomes nearly impossible when traffic is so bad on the freeway that everybody starts taking the off-freeway "shortcut" or "bypass" that your kids ride their bike on.
- theGnuMe 4y ago
  >Highways are typically built away from residential communities. lol, what?
  - listenallyall 4y ago
    What do you believe is the percentage of homes closer to a freeway than to a surface street?
- kdmccormick 4y ago
  This may be true in rural areas or car-centric cities, but in the Northeast US and many other dense parts of the world, freeways butt up against or even plow right through neighborhoods, especially lower-income ones. Until the late 90s, an elevated freeway ran through the middle of Boston. It's bad for safety, bad for health, and bad for happiness. In those places, it makes more long-term sense to invest in transit and bike infrastructure instead of inducing more demand for urban freeway bandwidth.
  - listenallyall 4y ago
    Bicycle riders ride on surface streets. For safety reasons, they should be in favor of diverting the maximum number of vehicles, especially large trucks and commercial vehicles, towards freeways and away from surface streets. Widening highways facilitates that.
jcims 4y ago
My brother has spent the last 25 years adding bandwidth to the local metro area. It most certainly occupies more physical space, sometimes at tremendous expense.
- throwaheyy 4y ago
  Ok, maybe it involves stringing up a new cable, onto poles already carrying many cables. That’s not even close to being comparable to widening highways.

silverpepsi 4y ago

Yep there should be a two dimensional metric of how many tax payers' needs were met and how well were they met. Serving more tax payers without an improved performance (time to destination) metric is still a win.

bobthepanda 4y ago
The cost benefit analysis is a generally accepted way of doing this. Interestingly enough, transit projects in the US are actually funded based on how competitive their CBA is, but highway projects are not and are funded via formulas defined in law by Congress.

repsilat 4y ago

I generally agree, but there are better versions of the argument. One of them is the Braess network paradox[1]. In short, under a model with simple game-theoretic assumptions about behaviour ("people find the shortcuts") and traffic/speed congestion functions an added road/connection can do more harm than good -- in the extreme case, slowing down every actor. The toy model may not actually be realistic, but I think reality might not be too different. Say the congestion delay function is smooth, and one added car doesn't change travel time much. How much does one of the new trips with the new infrastructure improve the life of the driver over the status quo? Very little: if travel times are the same, they only benefit to the extent that their trip would have slowed down traffic before. So generally you might say, - Adding the lanes but leaving behaviour the same would speed up traffic, improving global utility, - Letting traffic reach equilibrium (if speeds go back to what they were before -- big assumption) removes that benefit for existing travellers and doesn't much improve the life of new travellers, and is a net negative for global utility nearly equal in size to the earlier increase. - Maybe an argument for tolls? 1: https://en.m.wikipedia.org/wiki/Braess%27s_paradox https://en.m.wikipedia.org/wiki/Braess%27s_paradox

kurthr 4y ago

Even more than that, there are many places where there is a short narrow section of the same road (e.g. a 1 lane section connecting 2 lanes or 2 lane section connecting 3 lanes) that causes hugely inefficient usage. Fixing those is likely to be dramatically more cost/externality efficient than the alternatives. Also, those little squeezes are the very points where the Braess paradox actually shows up. Why let it?

wolpoli 4y ago

The concept of induced demand shifts the government from a role where it manages the supply of road to serve motorists, to a role where it exists to manage traffic. The critical differences in that the motorists are no longer meaningful stakeholders in the discussion, but merely as part of traffic.

tadfisher 4y ago
Those motorists overwhelmingly demand solutions to traffic. The folks losing their homes to freeway expansions are the ones who should have the largest stake.
- wolpoli 4y ago
  I agree that folks losing their homes to freeway expansions have stake in this. I am pointing out that the language shaped discourse against motorists. This is not the only example either. Motorists are compared with rats in other situations [1]. [1]: https://en.wikipedia.org/wiki/Rat_running https://en.wikipedia.org/wiki/Rat_running

bobthepanda 4y ago

The issue is not that induced demand exists (it exists for nearly every kind of travel) but that the cost-benefit ratio for highways is actually rather low, because highway lanes are so low capacity and fill up fast. (A standard metro line can easily carry 30-60k persons per direction per hour; the figure for a highway lane is 2.5k.) US highway transportation funding is not generally subject to cost effectiveness analysis but distributed according to formulas to the 50 states and funded at a 90-10 federal-local ratio, which is very different from how other modes of transportation are funded. Quite frankly, it is impossible to build your way out of highway congestion, without totally gutting American metropolitan areas, because there isn't just empty land in the middle of those for new highways. Which is also the root cause of most highway opposition these days, in existing areas; but new areas are not much better, in that usually this results in playing musical chairs with regional development rather than totally new net growth.

rayiner 4y ago
> but that the cost-benefit ratio for highways is actually rather low, because highway lanes are so low capacity and fill up fast. (A standard metro line can easily carry 30-60k persons per direction per hour; the figure for a highway lane is 2.5k.) That’s not the complete cost benefit calculation. A 4-lane highway costs $5-10 million per mile in suburban areas. Meanwhile, the DC Metro’s recent expansion through exurban Virginia mostly along an existing right of way cost $200 million per mile: https://www.heritage.org/transportation/commentary/washingtons-new-6-billion-metro-line-needs-simpler-solutions https://www.heritage.org/transportation/commentary/washingto.... So even if the rail carries three times as many people, it costs 20 to 40 times as much money per mile. That’s the cost side. On the benefit side, few places can saturate a subway line that carries 30,000 passengers per hour. Over the Thanksgiving weekend, just 5,000 people per day used the new Silver Line stops in Virginia. Even the design estimate of the Silver Line was 30,000 per day, and actual use has been a fraction of that. So the benefit side of the equation is a lot lower than the theoretical peak.
- bobthepanda 4y ago
  It makes more sense to compare like for like. The current project to expand I-66 in the DC suburbs of Virginia is $3.7B, which is $160M per mile along an existing right of way.

oefrha 4y ago

Instead of mindlessly deploying larger pipes to accommodate more HD video streams in MPEG-2, sometimes you design better compression in the form of AVC/HEVC.

anticensor 4y ago
Let me translate it into transport jargon: Instead of mindlessly deploying larger highways to accommodate more cars, sometimes you design better compression in the form of trains.
DesiLurker 4y ago
why not both? public transportation also need to be paired with good local connectivity (I have seen this first hand in sf bay-area). but then if local nimby's dont let local housing built and economic centers dont shift then all this means is people dont have a choice but to commute long distances (I have). I'll tell you the public transportation is definitely doable but it needs a lot more frequency and much better connectivity. definitely not the half assed way SV does it. Also time people spent doing same traveling between driving vs Public transportation needs to be comparable as in maybe 50% more not 2x or 3x (though that would be covered by my higher frequency & better connectivity comment but it needs to be a design consideration).

deleted 4y ago

[deleted]

stephen_g 4y ago

Obviously it's not a hard truth that no capacity improvement is worth it, but the idea of induced demand is describing something that is quantifiably true in many cases. And it's all about cost and physical space - that's why nobody worries much about induced demand in, say, bike lanes or train lines, because the route capacity of those modes is so much higher than car lanes. The issue at the end of the day is that, assuming a certain population density and a growing population, roads tend to become extremely expensive (because of the required property buybacks, etc.) while at the same time cars fundamentally take up too much space in urban/suburban areas for the number of people they tend to carry. (Obviously this is almost never an issue in rural areas, given the low population density). So it's not so much the issue that you couldn't theoretically build enough capacity, it's for most brownfield areas, you won't add enough capacity to fix traffic because of the huge cost - not to mention environmental destruction, or knocking down people's houses to replace with more and more roads, etc.. This is of course very different to, your example of internet bandwidth, where you can trivially increase the capacity by many multiples without taking up any more space physically. The closest analog in the transport world would be rail, which uses very little real estate compared to huge potential capacity. Given that fundamental issue (the cost and space that roads take up, and the fact that cars are one of the least volumetrically efficient modes of transport), what becomes observable is the ironic fact that the cities that tend to be best to drive in are the ones that have provided many good alternatives of good public transit, bikeways, etc. as opposed to the cities that were designed around the car.

stby 4y ago

You may want to read the article then, it's full of examples to prove that the concept is not silly. > No one's like "there's a new lane on the 5 and it's not moving any faster than it was before, I think I'll start taking it". The point here is that the new lane does actually "solve" traffic immediately after it has been opened. The improved travel times create the demand and eventually this leads to more congestion.