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I would contest that many roads are not built or expanded until they are needed and due to that the demand fills out the road on completion. If you were to take

by kenrikm 12y ago

I would contest that many roads are not built or expanded until they are needed and due to that the demand fills out the road on completion. If you were to take a 3 lane road that is at 70% capacity and make it 6 lanes I very highly doubt you would get a 6 lane road at 70% capacity. They reference a % thought an entire city, on a more Macro level a single bigger road can indeed ease congestion, though It may cause other roads leading into it to become congested. The only way out of the trap AFAIK would be to build excess capacity thought the entire system.

ChuckMcM 12y ago
Exactly this. Basically the 'demand' for driving is already > than the 'capacity' for driving, so adding capacity doesn't decrease congestion, it stays at 100%. This was made explicitly clear in the crash of 2000 when it felt like roughly 25% of the work force seems to have moved out of the Bay Area, traffic congestion got a lot less. If the theory of 'induced demand' was accurate, then traffic congestion would not have changed, and that would have been something worth writing about.
- darkxanthos 12y ago
  This exactly. This article didn't even try to objectively validate the report. It's also provably false in other areas like already not very busy roads in the high desert in SoCal. Add a new road to Apple Valley and I bet it gets used but very little there's just no demand. This report was highly biased since I'm sure no one built a road where people didn't need one and looked if demand were the same. Instead this is only about building roads where they were deemed to be critical enough to warrant a ton of spending and where the built out supply probably lags demand.
maxsilver 12y ago
> The only way out of the trap AFAIK would be to build excess capacity thought the entire system. I agree. This makes a lot more since. The authors are taking good data, but making a big leap on their assumption to the cause. Roads don't "create" traffic. New roads in most major cities are never built until the old ones are already 300-500% over capacity. If you wait until your 500% over capacity, and then double the lanes, your still way over capacity, so the old and new roads are still "congested". This traffic isn't "new" -- it was always there, you just couldn't see it, because a 200% over capacity road, and a 500% over capacity road, looks like the same gridlock from the sky.
- maxerickson 12y ago
  They count actual traffic though right? They aren't relying on qualitative assessments, they put those hose things by the side of the road.
- mattzito 12y ago
  Except that roads do create traffic. Your line of thinking was exactly what drove NYC's road construction boom in the 40s and 50s - new road is built, utilization briefly goes down, then, as soon as people realize that there's now a faster, more convenient way to get into the city, they start using it. Utilization goes back up. Critically, many of those people are people who might have taken mass transit or carpooled. They are literally new demand in the system driven by new capacity. Over a longer time period, there's an even deeper effect, where new roads and perceived availability of road transit drives more people to move to previously undesirable parts of metro areas, which increases population which increases demand.
  - maxsilver 12y ago
    > Except that roads do create traffic. - new road is built, utilization briefly goes down, then, as soon as people realize that there's now a faster, more convenient way to get into the city, they start using it. Utilization goes back up. That's not "new" traffic. Traffic was already critically underserved previously, and is now only majorly underserved. The original road was 500% over capacity, and now the new road lowers it to 300% over capacity. >They are literally new demand in the system driven by new capacity. No, the demand was always there. No one went out and bought a car because a new road was built. These are people who we're already underserved by transportation previously, but weren't counted (because demand so outstripped capacity that they couldn't be easily counted originally). > Critically, many of those people are people who might have taken mass transit or carpooled. This is a huge assumption. For instance, this can only even be possible in a handful of places like Chicago or NYC. There is no meaningful mass transit in the most of the major US cities to even pull traffic from. If public transit is a good option, people will take it regardless of how many roads exist. (Very few people purposely want to make life more expensive or more inconvenient for themselves). > as soon as people realize that there's now a faster, more convenient way to get into the city, they start using it. From what you've said, it sounds like your advocating for people to willingly make life more expensive and more inconvenient for themselves. Your saying "new roads make driving too convenient and nice, we should take roads out so driving becomes even more terrible than public transit already is. Force people to make a bad choice, to avoid a terrible one" - - There's absolutely no need to race-to-the-bottom on transportation. We should build more roads and build more public transit, simultaneously. When public transit becomes cheap and convenient, many people will willing choose it. For those who don't, new roads and additional capacity alleviates that problem as well. Your logic assumes that driving is inherently bad, and that we should "punish" drivers as a result. That's terrible, there's nothing wrong with driving, and there's no need to punish people for driving. There happen to be some bad externalities to driving (exhaust, traffic accidents), but those problems are being worked on (electric zero-emission cars, self driving cars, etc) - - What your advocating for sounds really dangerous. Imagine if we applied this logic to any other market: "The internet is congested. We can't just add fiber lines, if people had more internet speeds, they'd just use it up! We should destroy fiber lines, and cap all internet users to 1Mbps speeds, so that people start using the Postal Service and Blockbuster more often. " "We can't run more clean water to the bad part of town. It might 'drive more people to move to a previously undesirable part of the metro area'. We should keep the water system broken -- or actually, just start slowly cutting water off to that area. "
mattzito 12y ago
It's a lot more complicated than that, if I remember my research on this subject correctly. It is definitely true that in a perfectly abstract system that if your roads are 70% utilized across the board, and you double capacity, you won't stay at 70% capacity. However, what does happen is that when you take a road at 70% capacity and double it, so it has a lot more room, some people will move from other 70% utilized roads to your road, and yet more people will decide to drive instead of taking the bus or train, and the utilization of the whole system will remain largely flat at ~70%. This was seen time and time again in NYC, where even at the peak of construction of roadways in and out of the city under Robert Moses, every new bridge, tunnel, and highway was at >80% utilization within days or weeks of completion. IIRC, the total amount of major roadways in and around NYC was increased by 5-10x from the 1940s to 1950s, and yet traffic congestion and utilization actually increased over this time. It took a number of years of urban planning research to identify that as you increase the number of roads, more people opt to drive in lieu of mass transit or not making the trip at all. So, i would argue that in an abstract sense you are correct, but in the context of a major city, a single major road change does not ease congestion, as it simply changes traffic flows and increases demand.
- protonfish 12y ago
  % capacity and % utilization are measures of congestion - not of demand. If your roads are only meeting 10% of latent demand and you double their capacity, guess what? They will be just as congested as before. Leave it to "years of urban planning" to determine a proper solution is to make roads so poor that people decide not to use them.
  - gxs 12y ago
    Yeah, this explanation is so obvious to me, I just don't understand how they can try to spin it any other way. There are MILLLIONS of drivers in LA, I doubt we could build enough roads to make it so that there is never any traffic. I wonder if we're missing something here? Maybe the other and parent are leaving out some key details, but I doubt it.
    - 12y ago
gxs 12y ago
I came here to comment the same thing. This really sounds like an over engineered explanation and usually the simpler explanations turnS out to be more accurate. To use the author's own analogy, it's more like a pipe that is being overwhelmed being replaced by a slightly larger pipe that will continue to be overwhelmed. That said, I hope it encourages people to find creative ways of solving the traffic problem.
toddmorey 12y ago
There's another question that we are starting to battle recently: how much actual capacity can we honestly add to the road system? Near my parents' home, there's an intersection of a 18 lanes (!) of highway + access road crossing over a 9-lane surface street. I just don't know how you grow that any further, without the prohibitively expensive option of more vertical stacking. I've always thought of our current car-based transportation system to be amazingly inefficient when measured in energy consumption per passenger and travel time. But I'm noticing it's also extremely greedy with land use.
- warfangle 12y ago
  It's not just greedy with land use: it's literally hostile to humanity. In places in the US with a large driving culture it is almost a death wish to walk anywhere (because none of the drivers are expecting to have to watch out for a pedestrian).
forkandwait 12y ago
I think you are arguing "a priori" - you have a set of given principles and then you derive conclusions. While very powerful when done by smart people, a priori reasoning is often wrong, and should always be trumped by real data. I think one of the points of the article is that the data point to a flaw in the way we intuitively reason about the situation.
Shivetya 12y ago
Well they tend to focus on one road at a time, either ignore the feeders or the effect the newly expanded feeder has on surrounding roads. Common around where I live is expanding two lane roads to three lanes and going back to two the closer to the city you get.

by kenrikm 12y ago

ChuckMcM 12y ago

Exactly this. Basically the 'demand' for driving is already > than the 'capacity' for driving, so adding capacity doesn't decrease congestion, it stays at 100%. This was made explicitly clear in the crash of 2000 when it felt like roughly 25% of the work force seems to have moved out of the Bay Area, traffic congestion got a lot less. If the theory of 'induced demand' was accurate, then traffic congestion would not have changed, and that would have been something worth writing about.

darkxanthos 12y ago
This exactly. This article didn't even try to objectively validate the report. It's also provably false in other areas like already not very busy roads in the high desert in SoCal. Add a new road to Apple Valley and I bet it gets used but very little there's just no demand. This report was highly biased since I'm sure no one built a road where people didn't need one and looked if demand were the same. Instead this is only about building roads where they were deemed to be critical enough to warrant a ton of spending and where the built out supply probably lags demand.

maxsilver 12y ago

> The only way out of the trap AFAIK would be to build excess capacity thought the entire system. I agree. This makes a lot more since. The authors are taking good data, but making a big leap on their assumption to the cause. Roads don't "create" traffic. New roads in most major cities are never built until the old ones are already 300-500% over capacity. If you wait until your 500% over capacity, and then double the lanes, your still way over capacity, so the old and new roads are still "congested". This traffic isn't "new" -- it was always there, you just couldn't see it, because a 200% over capacity road, and a 500% over capacity road, looks like the same gridlock from the sky.

maxerickson 12y ago
They count actual traffic though right? They aren't relying on qualitative assessments, they put those hose things by the side of the road.
mattzito 12y ago
Except that roads do create traffic. Your line of thinking was exactly what drove NYC's road construction boom in the 40s and 50s - new road is built, utilization briefly goes down, then, as soon as people realize that there's now a faster, more convenient way to get into the city, they start using it. Utilization goes back up. Critically, many of those people are people who might have taken mass transit or carpooled. They are literally new demand in the system driven by new capacity. Over a longer time period, there's an even deeper effect, where new roads and perceived availability of road transit drives more people to move to previously undesirable parts of metro areas, which increases population which increases demand.
- maxsilver 12y ago
  > Except that roads do create traffic. - new road is built, utilization briefly goes down, then, as soon as people realize that there's now a faster, more convenient way to get into the city, they start using it. Utilization goes back up. That's not "new" traffic. Traffic was already critically underserved previously, and is now only majorly underserved. The original road was 500% over capacity, and now the new road lowers it to 300% over capacity. >They are literally new demand in the system driven by new capacity. No, the demand was always there. No one went out and bought a car because a new road was built. These are people who we're already underserved by transportation previously, but weren't counted (because demand so outstripped capacity that they couldn't be easily counted originally). > Critically, many of those people are people who might have taken mass transit or carpooled. This is a huge assumption. For instance, this can only even be possible in a handful of places like Chicago or NYC. There is no meaningful mass transit in the most of the major US cities to even pull traffic from. If public transit is a good option, people will take it regardless of how many roads exist. (Very few people purposely want to make life more expensive or more inconvenient for themselves). > as soon as people realize that there's now a faster, more convenient way to get into the city, they start using it. From what you've said, it sounds like your advocating for people to willingly make life more expensive and more inconvenient for themselves. Your saying "new roads make driving too convenient and nice, we should take roads out so driving becomes even more terrible than public transit already is. Force people to make a bad choice, to avoid a terrible one" - - There's absolutely no need to race-to-the-bottom on transportation. We should build more roads and build more public transit, simultaneously. When public transit becomes cheap and convenient, many people will willing choose it. For those who don't, new roads and additional capacity alleviates that problem as well. Your logic assumes that driving is inherently bad, and that we should "punish" drivers as a result. That's terrible, there's nothing wrong with driving, and there's no need to punish people for driving. There happen to be some bad externalities to driving (exhaust, traffic accidents), but those problems are being worked on (electric zero-emission cars, self driving cars, etc) - - What your advocating for sounds really dangerous. Imagine if we applied this logic to any other market: "The internet is congested. We can't just add fiber lines, if people had more internet speeds, they'd just use it up! We should destroy fiber lines, and cap all internet users to 1Mbps speeds, so that people start using the Postal Service and Blockbuster more often. " "We can't run more clean water to the bad part of town. It might 'drive more people to move to a previously undesirable part of the metro area'. We should keep the water system broken -- or actually, just start slowly cutting water off to that area. "

mattzito 12y ago

It's a lot more complicated than that, if I remember my research on this subject correctly. It is definitely true that in a perfectly abstract system that if your roads are 70% utilized across the board, and you double capacity, you won't stay at 70% capacity. However, what does happen is that when you take a road at 70% capacity and double it, so it has a lot more room, some people will move from other 70% utilized roads to your road, and yet more people will decide to drive instead of taking the bus or train, and the utilization of the whole system will remain largely flat at ~70%. This was seen time and time again in NYC, where even at the peak of construction of roadways in and out of the city under Robert Moses, every new bridge, tunnel, and highway was at >80% utilization within days or weeks of completion. IIRC, the total amount of major roadways in and around NYC was increased by 5-10x from the 1940s to 1950s, and yet traffic congestion and utilization actually increased over this time. It took a number of years of urban planning research to identify that as you increase the number of roads, more people opt to drive in lieu of mass transit or not making the trip at all. So, i would argue that in an abstract sense you are correct, but in the context of a major city, a single major road change does not ease congestion, as it simply changes traffic flows and increases demand.

protonfish 12y ago
% capacity and % utilization are measures of congestion - not of demand. If your roads are only meeting 10% of latent demand and you double their capacity, guess what? They will be just as congested as before. Leave it to "years of urban planning" to determine a proper solution is to make roads so poor that people decide not to use them.
- gxs 12y ago
  Yeah, this explanation is so obvious to me, I just don't understand how they can try to spin it any other way. There are MILLLIONS of drivers in LA, I doubt we could build enough roads to make it so that there is never any traffic. I wonder if we're missing something here? Maybe the other and parent are leaving out some key details, but I doubt it.
  - 12y ago

gxs 12y ago

I came here to comment the same thing. This really sounds like an over engineered explanation and usually the simpler explanations turnS out to be more accurate. To use the author's own analogy, it's more like a pipe that is being overwhelmed being replaced by a slightly larger pipe that will continue to be overwhelmed. That said, I hope it encourages people to find creative ways of solving the traffic problem.

toddmorey 12y ago

There's another question that we are starting to battle recently: how much actual capacity can we honestly add to the road system? Near my parents' home, there's an intersection of a 18 lanes (!) of highway + access road crossing over a 9-lane surface street. I just don't know how you grow that any further, without the prohibitively expensive option of more vertical stacking. I've always thought of our current car-based transportation system to be amazingly inefficient when measured in energy consumption per passenger and travel time. But I'm noticing it's also extremely greedy with land use.

warfangle 12y ago
It's not just greedy with land use: it's literally hostile to humanity. In places in the US with a large driving culture it is almost a death wish to walk anywhere (because none of the drivers are expecting to have to watch out for a pedestrian).

forkandwait 12y ago

I think you are arguing "a priori" - you have a set of given principles and then you derive conclusions. While very powerful when done by smart people, a priori reasoning is often wrong, and should always be trumped by real data. I think one of the points of the article is that the data point to a flaw in the way we intuitively reason about the situation.

Shivetya 12y ago

Well they tend to focus on one road at a time, either ignore the feeders or the effect the newly expanded feeder has on surrounding roads. Common around where I live is expanding two lane roads to three lanes and going back to two the closer to the city you get.