5 ms·

And in this corner: Braess's Paradox, "the observation that adding one or more roads to a road network can slow down overall traffic flow through it." https://

by fernly 5y ago

And in this corner: Braess's Paradox, "the observation that adding one or more roads to a road network can slow down overall traffic flow through it." https://en.wikipedia.org/wiki/Braess%27s_paradox https://en.wikipedia.org/wiki/Braess%27s_paradox

wahern 5y ago
I can't find the paper now, but when researching mesh networks and onion routing circa 2001-2005 I remember a paper which showed that in a distributed, decentralized mesh network (plus or minus some other constraints that may or may not have mattered, like uniformity) each additional node increased aggregate throughput, but the increase asymptotically approached zero.
- barathr 5y ago
  I don't know if it was this paper, but this was a classic piece of research on that topic from that era: https://doi.org/10.1145/381677.381684 https://doi.org/10.1145/381677.381684
BeefWellington 5y ago
Along a similar vein: https://nautil.us/issue/13/symmetry/want-to-get-out-alive-follow-the-ants https://nautil.us/issue/13/symmetry/want-to-get-out-alive-fo... Essentially, by obstructing emergency exits they can work better to channel people out.
kypro 5y ago
They have taken this approach in my city arguing improving the road network will not improve congestion and if anything reducing the number of roads is what's needed. What I don't understand about this argument is that the point surely isn't to solve for congestion or travel time, but for transport efficiency, or at a higher level, economic output, as transport efficiency likely correlates with that. Even if the number of cars on the road would double if you had twice as many roads, if the number of people now able to travel to their destination would also approximately double it would seem to me that this would be preferable? Also does this argument ever get made for any other form of transport? For example when subway systems don't have enough capacity doesn't this paradox apply? Is it therefore pointless to expand the capacity of subway systems because doing so would just increase their use? It's also interesting to me that this logic isn't ever used to argue against building new homes because it seems it would apply far more to that. I can only "consume" one road or subway service at a time, but my consumption potential of real-estate is unlimited. If we follow this logic then as you build more homes the demand for homes will increase without an upper limit, therefore building homes to solve the problem of a housing shortage is always a pointless endeavour and if anything houses should be demolished to reduce the demand for housing. Honestly, I haven't looked into any of this that much so I'm sure I'm demonstrating the Dunning–Kruger effect right now, but how this paradox is used politically always confused me. It just doesn't seem to make much sense to me to argue we need to remove roads to fix congestion, while also arguing to build houses to fix home shortages, but this is what the politicians here do.
- MereInterest 5y ago
  There's a number of key differences, mostly in how things scale with increased use. * Car transit is typically scaled through increased space allocation. Public transit is typically scaled through increased utilization of the same space. * Car transit is limited at about 2000 vehicles/lane/hour. Public transit is mainly limited by the number of buses/trains on a route. (e.g. A typical bus can carry 30-100 people. Replacing a lane of car transit with a dedicated bus lane drastically increases the throughput of that lane.) * If the number of highway lanes are doubled, followed by induced demand using that capacity, the result is a much less enjoyable experience driving. If the frequency of buses doubles, followed by induced demand using that capacity, the result is a much more enjoyable experience taking the bus, as the wait for the next bus is shorter. * There's a phase transition in public transit utilization that happens when buses/trains/subways arrive more often than once every 15 minutes or so. If a bus arrives once every hour, you need to carefully plan your day around that particular bus, arrive early to make sure you don't miss it, and waste a lot of time waiting. If a bus arrives once every 10 minutes, there's no need to plan ahead, and you just get on whichever bus arrives next. The Youtube channel "Oh the Urbanity" had a pretty good video on induced demand as it applies to both car transit and public transit [0], that I highly recommend. Most everything by the "Not Just Bikes" channel [1] is also pretty good. [0] https://www.youtube.com/watch?v=8wlld3Z9wRc https://www.youtube.com/watch?v=8wlld3Z9wRc [1] https://www.youtube.com/c/NotJustBikes/videos https://www.youtube.com/c/NotJustBikes/videos
  - kypro 5y ago
    Thank you so much. That video basically addressed my exact confusion! The internet is amazing. I think I'm correct in thinking this paradox does apply to other modes of transport such as subways, but that by itself doesn't mean that we should therefore build more roads because in general infrastructure spending would be better allocated to other modes of transport for numerous reasons. I do agree with that argument, but it seems there would be nuances there. I'd agree it's generally more efficient in the inner city, but less so as population density decreases. In areas with low population density the car is probably by far the best mode of transportation and there its use should probably be accepted. I think my confusion comes from how it's often sold as a black and white thing politically where, `car=bad` because this clearly isn't true as general rule. If the argument is simply that within densely populated areas the use of public transportation should be promoted over extra capacity for cars then I completely agree, but where I live I would argue some questionable city planning decisions have been made. Specifically, lanes have been removed from roads to make way for bike lanes and speed limits have been reduced almost universally. While I'm all for promoting cycling these bike lanes go almost entirely unused because it's very hilly and things are too far away for cycling to be a practical mode of transportation in most cases here. In this case the pros and cons don't appear to add up and I suspect the city planners are probably just out of touch with the differing transportation requirements between where they are in the inner city and in areas such as mine.

by fernly 5y ago

wahern 5y ago

I can't find the paper now, but when researching mesh networks and onion routing circa 2001-2005 I remember a paper which showed that in a distributed, decentralized mesh network (plus or minus some other constraints that may or may not have mattered, like uniformity) each additional node increased aggregate throughput, but the increase asymptotically approached zero.

barathr 5y ago
I don't know if it was this paper, but this was a classic piece of research on that topic from that era: https://doi.org/10.1145/381677.381684 https://doi.org/10.1145/381677.381684

BeefWellington 5y ago

Along a similar vein: https://nautil.us/issue/13/symmetry/want-to-get-out-alive-follow-the-ants https://nautil.us/issue/13/symmetry/want-to-get-out-alive-fo... Essentially, by obstructing emergency exits they can work better to channel people out.

kypro 5y ago

They have taken this approach in my city arguing improving the road network will not improve congestion and if anything reducing the number of roads is what's needed. What I don't understand about this argument is that the point surely isn't to solve for congestion or travel time, but for transport efficiency, or at a higher level, economic output, as transport efficiency likely correlates with that. Even if the number of cars on the road would double if you had twice as many roads, if the number of people now able to travel to their destination would also approximately double it would seem to me that this would be preferable? Also does this argument ever get made for any other form of transport? For example when subway systems don't have enough capacity doesn't this paradox apply? Is it therefore pointless to expand the capacity of subway systems because doing so would just increase their use? It's also interesting to me that this logic isn't ever used to argue against building new homes because it seems it would apply far more to that. I can only "consume" one road or subway service at a time, but my consumption potential of real-estate is unlimited. If we follow this logic then as you build more homes the demand for homes will increase without an upper limit, therefore building homes to solve the problem of a housing shortage is always a pointless endeavour and if anything houses should be demolished to reduce the demand for housing. Honestly, I haven't looked into any of this that much so I'm sure I'm demonstrating the Dunning–Kruger effect right now, but how this paradox is used politically always confused me. It just doesn't seem to make much sense to me to argue we need to remove roads to fix congestion, while also arguing to build houses to fix home shortages, but this is what the politicians here do.

MereInterest 5y ago
There's a number of key differences, mostly in how things scale with increased use. * Car transit is typically scaled through increased space allocation. Public transit is typically scaled through increased utilization of the same space. * Car transit is limited at about 2000 vehicles/lane/hour. Public transit is mainly limited by the number of buses/trains on a route. (e.g. A typical bus can carry 30-100 people. Replacing a lane of car transit with a dedicated bus lane drastically increases the throughput of that lane.) * If the number of highway lanes are doubled, followed by induced demand using that capacity, the result is a much less enjoyable experience driving. If the frequency of buses doubles, followed by induced demand using that capacity, the result is a much more enjoyable experience taking the bus, as the wait for the next bus is shorter. * There's a phase transition in public transit utilization that happens when buses/trains/subways arrive more often than once every 15 minutes or so. If a bus arrives once every hour, you need to carefully plan your day around that particular bus, arrive early to make sure you don't miss it, and waste a lot of time waiting. If a bus arrives once every 10 minutes, there's no need to plan ahead, and you just get on whichever bus arrives next. The Youtube channel "Oh the Urbanity" had a pretty good video on induced demand as it applies to both car transit and public transit [0], that I highly recommend. Most everything by the "Not Just Bikes" channel [1] is also pretty good. [0] https://www.youtube.com/watch?v=8wlld3Z9wRc https://www.youtube.com/watch?v=8wlld3Z9wRc [1] https://www.youtube.com/c/NotJustBikes/videos https://www.youtube.com/c/NotJustBikes/videos
- kypro 5y ago
  Thank you so much. That video basically addressed my exact confusion! The internet is amazing. I think I'm correct in thinking this paradox does apply to other modes of transport such as subways, but that by itself doesn't mean that we should therefore build more roads because in general infrastructure spending would be better allocated to other modes of transport for numerous reasons. I do agree with that argument, but it seems there would be nuances there. I'd agree it's generally more efficient in the inner city, but less so as population density decreases. In areas with low population density the car is probably by far the best mode of transportation and there its use should probably be accepted. I think my confusion comes from how it's often sold as a black and white thing politically where, `car=bad` because this clearly isn't true as general rule. If the argument is simply that within densely populated areas the use of public transportation should be promoted over extra capacity for cars then I completely agree, but where I live I would argue some questionable city planning decisions have been made. Specifically, lanes have been removed from roads to make way for bike lanes and speed limits have been reduced almost universally. While I'm all for promoting cycling these bike lanes go almost entirely unused because it's very hilly and things are too far away for cycling to be a practical mode of transportation in most cases here. In this case the pros and cons don't appear to add up and I suspect the city planners are probably just out of touch with the differing transportation requirements between where they are in the inner city and in areas such as mine.