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This is called ‘induced demand’. Surprisingly, the opposite happens when you remove road capacity - which is called ‘traffic evaporation’. It’s why taking road

This is called ‘induced demand’. Surprisingly, the opposite happens when you remove road capacity - which is called ‘traffic evaporation’. It’s why taking road space from cars and reallocating it to bicycles is often more successful than predicted: https://nacto.org/docs/usdg/disappearing_traffic_cairns.pdf https://nacto.org/docs/usdg/disappearing_traffic_cairns.pdf

kqr 5y ago
Removing capacity from infrastructure is a solution that works when you want to discourage use of that infrastructure. If that's not the case, I only know of one other solution: charge directly for usage. That way you can set the price such that demand stays at a high level, but at one supported by maximum available capacity. If someone knows of a different solution, I'd like to know -- I have an induced demand problem in a type of infrastructure that I would like to operate at high capacity, and charging for it would be unconventional to the point of making it hard to find support for that solution.
- goodpoint 5y ago
  Charging money for access to transportation is very politically biased: people with low or no income are effectively denied transportation while people with high income are not discouraged. This is how slums are created. > If someone knows of a different solution, I'd like to know Some cities have areas that allow unlimited access to locals and deliveries and limited access to others (X times per year)
  - kqr 5y ago
    Yes, that's a problem. I've debated with myself over what would be a fair division of "limited access" in my case but not arrived at a satisfactory solution. Anything I can think of will devolve into an inefficient, sucky, inofficial market. (This is why I'm contemplating an efficient, less sucky, official market in the first place.) To be clear: the infrastructure I'm working on isn't transport, but it'd still be odd to only allow paying users. I was thinking two similar copies of this piece infrastructure, where one is priced to avoid congestion, and the other will be as congested as induced demand allows. I'd like the discussion to stay general because I suspect any solutions will be reusable.
    - goodpoint 5y ago
      ...another example is the bus/metro transportation card: in many cities you get charged both based on your income bracket, usage pattern and things like being retired/student/young/adult and so on
      - kqr 5y ago
        This is a great point and one applicable to my case as well. I have an obvious proxy for income bracket to even out the playing field. Thanks!
  - supertrope 5y ago
    Are people entitled to free roads? If yes then the electorate will not care that fuel taxes and registration fees don't cover road maintenance costs - it's a dignity not a price. If not then all roads should be toll roads or cars can be taxed per mile via odometer readings. Making things free at the point of use is not always the best way to help the poor or public. The inefficiency of no charge first come first serve could outweigh equity benefits. Having everyone pay in time (traffic jams) is a large hidden cost. Time is valuable even for those who lack money. The US Department of Transportation came up with a benchmark of $12.25/hour (50% of median household income) to evaluate the expected time savings of proposed transportation projects (2014). With free roads only time, fuel, and vehicle depreciation are considered. Roads are considered zero cost. There's minimal consideration of mass transit, carpooling, or moving closer to work. Just demands to add another lane and more parking everywhere. If roads were tolled or a lane was re-allocated to buses that could help poor people by making carpooling or riding a bus a realistic lower cost alternative to owning a car (or second car). Carpooling is a great example of how tolls incentivize high efficiency: 2 coworkers coming from the same neighborhood can cut their vehicle ownership expenses, the toll only hits half as hard, the people/hour throughput of the road goes up, and they take up less parking. Two people get to avoid congestion doubling time savings. Infrastructure is always shared. There are hard normative questions about how capacity should be allocated, and who should be subsidized. Making it free at the point of use doesn't eliminate those trade off questions.
    - goodpoint 5y ago
      I don't understand what point you are trying to make. > If not then all roads should be toll roads or cars can be taxed per mile via odometer readings ...or you tax the combination of car usage and fuel efficiency by taxing fuel consumption. Which is already done with steep taxes on fuel sale in some countries and it's discouraging car use. For some people.
      - supertrope 5y ago
        Charging for road use is not necessarily anti-poor people.
londons_explore 5y ago
I assume that both traffic evaporation and induced demand have a knock on effect elsewhere in the economy. When a road is closed fewer people can get from A to B easily, meaning less trade in shops near there, people taking less-optimal nearby jobs because they can't commute to a better job further away, delivery companies using two trucks and drivers instead of one, etc. Each individual sees a small disadvantage when a bridge is closed, but the overall economic effect might be very substantial, and hard to measure.
- adrianN 5y ago
  Traffic and the economy are complex enough that the answer is "it depends" most of the time. Generally when you close a street to cars pedestrian traffic increases. Pedestrians tend to spend a lot more money on a street that cars driving by. Cafes tend to flourish.
  - londons_explore 5y ago
    I guess the way to model that is to model the traffic and economic effects of a closed road, and separately model the economic benefits of a pedestrian street. Add the two together, and you have your result.
  - goodpoint 5y ago
    On top of that, low-walkability car-intensive cities strongly correlate with increased street crime and mental illness (depression, social isolation). In various countries sprawls, shopping districts and office-only areas are prohibited by building regulations in order to create mixed areas where people can live/shop/work and build local communities.
    - greggman3 5y ago
      > low-walkability car-intensive cities strongly correlate with increased street crime Do you have any links? that goes entirely against my intuition. SF is generally considered walkable and has high street crime. I'm pretty sure the same is true for NYC, Paris, Berlin, other highly walkable cities where as say Irvine, Brea, (E.T. like neighborhoods that require a car to do anything) have low-street crime. Update: The first 2 hits I found on google found higher walkability correlated with more crime https://journals.sagepub.com/doi/abs/10.1177/0013916520921843?journalCode=eaba https://journals.sagepub.com/doi/abs/10.1177/001391652092184... https://link.springer.com/article/10.1057/s41284-018-00161-7 https://link.springer.com/article/10.1057/s41284-018-00161-7

kqr 5y ago

Removing capacity from infrastructure is a solution that works when you want to discourage use of that infrastructure. If that's not the case, I only know of one other solution: charge directly for usage. That way you can set the price such that demand stays at a high level, but at one supported by maximum available capacity. If someone knows of a different solution, I'd like to know -- I have an induced demand problem in a type of infrastructure that I would like to operate at high capacity, and charging for it would be unconventional to the point of making it hard to find support for that solution.

goodpoint 5y ago
Charging money for access to transportation is very politically biased: people with low or no income are effectively denied transportation while people with high income are not discouraged. This is how slums are created. > If someone knows of a different solution, I'd like to know Some cities have areas that allow unlimited access to locals and deliveries and limited access to others (X times per year)
- kqr 5y ago
  Yes, that's a problem. I've debated with myself over what would be a fair division of "limited access" in my case but not arrived at a satisfactory solution. Anything I can think of will devolve into an inefficient, sucky, inofficial market. (This is why I'm contemplating an efficient, less sucky, official market in the first place.) To be clear: the infrastructure I'm working on isn't transport, but it'd still be odd to only allow paying users. I was thinking two similar copies of this piece infrastructure, where one is priced to avoid congestion, and the other will be as congested as induced demand allows. I'd like the discussion to stay general because I suspect any solutions will be reusable.
  - goodpoint 5y ago
    ...another example is the bus/metro transportation card: in many cities you get charged both based on your income bracket, usage pattern and things like being retired/student/young/adult and so on
    - kqr 5y ago
      This is a great point and one applicable to my case as well. I have an obvious proxy for income bracket to even out the playing field. Thanks!
- supertrope 5y ago
  Are people entitled to free roads? If yes then the electorate will not care that fuel taxes and registration fees don't cover road maintenance costs - it's a dignity not a price. If not then all roads should be toll roads or cars can be taxed per mile via odometer readings. Making things free at the point of use is not always the best way to help the poor or public. The inefficiency of no charge first come first serve could outweigh equity benefits. Having everyone pay in time (traffic jams) is a large hidden cost. Time is valuable even for those who lack money. The US Department of Transportation came up with a benchmark of $12.25/hour (50% of median household income) to evaluate the expected time savings of proposed transportation projects (2014). With free roads only time, fuel, and vehicle depreciation are considered. Roads are considered zero cost. There's minimal consideration of mass transit, carpooling, or moving closer to work. Just demands to add another lane and more parking everywhere. If roads were tolled or a lane was re-allocated to buses that could help poor people by making carpooling or riding a bus a realistic lower cost alternative to owning a car (or second car). Carpooling is a great example of how tolls incentivize high efficiency: 2 coworkers coming from the same neighborhood can cut their vehicle ownership expenses, the toll only hits half as hard, the people/hour throughput of the road goes up, and they take up less parking. Two people get to avoid congestion doubling time savings. Infrastructure is always shared. There are hard normative questions about how capacity should be allocated, and who should be subsidized. Making it free at the point of use doesn't eliminate those trade off questions.
  - goodpoint 5y ago
    I don't understand what point you are trying to make. > If not then all roads should be toll roads or cars can be taxed per mile via odometer readings ...or you tax the combination of car usage and fuel efficiency by taxing fuel consumption. Which is already done with steep taxes on fuel sale in some countries and it's discouraging car use. For some people.
    - supertrope 5y ago
      Charging for road use is not necessarily anti-poor people.

londons_explore 5y ago

I assume that both traffic evaporation and induced demand have a knock on effect elsewhere in the economy. When a road is closed fewer people can get from A to B easily, meaning less trade in shops near there, people taking less-optimal nearby jobs because they can't commute to a better job further away, delivery companies using two trucks and drivers instead of one, etc. Each individual sees a small disadvantage when a bridge is closed, but the overall economic effect might be very substantial, and hard to measure.

adrianN 5y ago
Traffic and the economy are complex enough that the answer is "it depends" most of the time. Generally when you close a street to cars pedestrian traffic increases. Pedestrians tend to spend a lot more money on a street that cars driving by. Cafes tend to flourish.
- londons_explore 5y ago
  I guess the way to model that is to model the traffic and economic effects of a closed road, and separately model the economic benefits of a pedestrian street. Add the two together, and you have your result.
- goodpoint 5y ago
  On top of that, low-walkability car-intensive cities strongly correlate with increased street crime and mental illness (depression, social isolation). In various countries sprawls, shopping districts and office-only areas are prohibited by building regulations in order to create mixed areas where people can live/shop/work and build local communities.
  - greggman3 5y ago
    > low-walkability car-intensive cities strongly correlate with increased street crime Do you have any links? that goes entirely against my intuition. SF is generally considered walkable and has high street crime. I'm pretty sure the same is true for NYC, Paris, Berlin, other highly walkable cities where as say Irvine, Brea, (E.T. like neighborhoods that require a car to do anything) have low-street crime. Update: The first 2 hits I found on google found higher walkability correlated with more crime https://journals.sagepub.com/doi/abs/10.1177/0013916520921843?journalCode=eaba https://journals.sagepub.com/doi/abs/10.1177/001391652092184... https://link.springer.com/article/10.1057/s41284-018-00161-7 https://link.springer.com/article/10.1057/s41284-018-00161-7