4 ms·

Simple explanation: when you win five minutes by switching from road A to road B, other drivers on road B might lose more than five minutes in total from the ex

Simple explanation: when you win five minutes by switching from road A to road B, other drivers on road B might lose more than five minutes in total from the extra congestion you cause. So the total time spent by all drivers will increase, and so will average time (if number of drivers is constant). So removing some connections from the road network, to prevent some drivers from optimizing their route, can reduce average driving time.

martin-adams 8y ago
Thank you for that explanation. In a way it reminds me of the cost of context switching. Sure, it seems quicker to do a task right now, but the overall cost will go up because of what you left behind.
dorfsmay 8y ago
From reading the article, they do not fix the numbers of cars, so it is likely that the number of cars has a greater effect on flow. Improvement in roads always lead to more cars, beyond what was expected. Entire suburbs get created when roads improve! From the article: "the removal of main roads does not cause deterioration of traffic .../... some motorized travels are not transferred on public transport and simply disappear ("evaporate")."
mannykannot 8y ago
Furthermore, when a driver chooses to take the new route, this does not create any opportunity for the drivers disadvantaged by this choice to do better for themselves (they also have the option of switching to the new route themselves, but that opportunity was created by the creation of the new route, not by the responses to it by other drivers.) This paradox may have some relevance to the effect of navigation apps, especially those that attempt to route around congestion, as they effectively create routes in the sense that the vast majority of drivers would not have considered using them without the app.
- hota_mazi 8y ago
  I wonder if current navigation apps are smart enough to only propose a new route to a portion of the total number of drivers in that location. Ultimately, the only way to have optimal flow is to delegate all itinerary decisions to a central authority...
  - PKop 8y ago
    At the very least, the estimated time for given routes would update dynamically, as a proposed alternative route became less efficient.
  - toast0 8y ago
    Have you noticed how good the time estimates have gotten? Clearly they're streering other traffic out of or into the way to keep it even.
    - ashtonbaker 8y ago
      I started noticing this very abruptly - that Google no longer redirects me from congested roadways to low-traffic parallel roads. Now, as soon as I take the exit to a less congested road, my estimated drive time might drop by 5-10 minutes, so clearly Google knows that it isn't sending me down the optimal route. I don't think this used to be the case.
      - mannykannot 8y ago
        Interesting - I noticed recently, for the first time, that when I modified a 'fastest' proposed route using local knowledge, I found the predicted time dropped, and that has happened several time since. This may be the result of better predictive modeling, and particularly in recognizing that dumping a lot of traffic into a low-capacity route is pointless. It is probably also a political response to the fact that residential areas don't like having a lot of traffic routed through them, and are pressing for the power to regulate it. Better predictions could also explain toast0's observations even when global optimization is not being attempted.

martin-adams 8y ago

Thank you for that explanation. In a way it reminds me of the cost of context switching. Sure, it seems quicker to do a task right now, but the overall cost will go up because of what you left behind.

dorfsmay 8y ago

From reading the article, they do not fix the numbers of cars, so it is likely that the number of cars has a greater effect on flow. Improvement in roads always lead to more cars, beyond what was expected. Entire suburbs get created when roads improve! From the article: "the removal of main roads does not cause deterioration of traffic .../... some motorized travels are not transferred on public transport and simply disappear ("evaporate")."

mannykannot 8y ago

Furthermore, when a driver chooses to take the new route, this does not create any opportunity for the drivers disadvantaged by this choice to do better for themselves (they also have the option of switching to the new route themselves, but that opportunity was created by the creation of the new route, not by the responses to it by other drivers.) This paradox may have some relevance to the effect of navigation apps, especially those that attempt to route around congestion, as they effectively create routes in the sense that the vast majority of drivers would not have considered using them without the app.

hota_mazi 8y ago
I wonder if current navigation apps are smart enough to only propose a new route to a portion of the total number of drivers in that location. Ultimately, the only way to have optimal flow is to delegate all itinerary decisions to a central authority...
- PKop 8y ago
  At the very least, the estimated time for given routes would update dynamically, as a proposed alternative route became less efficient.
- toast0 8y ago
  Have you noticed how good the time estimates have gotten? Clearly they're streering other traffic out of or into the way to keep it even.
  - ashtonbaker 8y ago
    I started noticing this very abruptly - that Google no longer redirects me from congested roadways to low-traffic parallel roads. Now, as soon as I take the exit to a less congested road, my estimated drive time might drop by 5-10 minutes, so clearly Google knows that it isn't sending me down the optimal route. I don't think this used to be the case.
    - mannykannot 8y ago
      Interesting - I noticed recently, for the first time, that when I modified a 'fastest' proposed route using local knowledge, I found the predicted time dropped, and that has happened several time since. This may be the result of better predictive modeling, and particularly in recognizing that dumping a lot of traffic into a low-capacity route is pointless. It is probably also a political response to the fact that residential areas don't like having a lot of traffic routed through them, and are pressing for the power to regulate it. Better predictions could also explain toast0's observations even when global optimization is not being attempted.