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Could a traffic jam in 1 road spread across all roads?

  1. Nov 21, 2016 #1
    I have been in situations where low traffic leads in just a few seconds to a traffic jam both on the streets and on the highway.

    https://tse1.mm.bing.net/th?&id=OIP.Mcb0d8b1940e2cf082bb67ef045975841o0&w=300&h=168&c=0&pid=1.9&rs=0&p=0&r=0 [Broken]
    Traffic jam on street

    https://tse1.mm.bing.net/th?&id=OIP.M835e36a3e28bd3c1f16ba7bada76f5bfo0&w=300&h=199&c=0&pid=1.9&rs=0&p=0&r=0 [Broken]
    Traffic jam on highway

    I most commonly see traffic jams on the highways and low traffic on the streets. But those traffic jams seem like they would lead to more and more traffic jams and spread across all the roads. However it is usually localized. I mean for example when I get home from Columbus State downtown, the first highway that comes up that I go on is I-71. This highway that goes from downtown Columbus to uptown Columbus always has some bad traffic but when going home from college, there is often a traffic jam on this highway. I get onto I-270 and there is no more traffic jam.

    Why does the traffic jam not spread and cause more traffic jams and could a traffic jam spread throughout a network of roads no matter how widespread the roads are(city, state, country, continent)?
    Last edited by a moderator: May 8, 2017
  2. jcsd
  3. Nov 21, 2016 #2


    Staff: Mentor

    In reality all kind of results are possible as well as realized in certain conditions. So without any further specification there is no simple answer to it. The problem itself is subject to various fields of research. E.g. for the usual morning traffic jam, highways with a low average speed are still faster than roads of lower priority and often only subjective higher average speed. However, if there are special events, traffic jam might spread to all roads. One example I experienced has been the occasion of a solar eclipse which was expected to be best seen from about 100 miles south. So really many people added up to the usual already heavy traffic load and literally all south bounded roads had been overcrowded.

    So the entire situation is really depending on many variables.
  4. Nov 21, 2016 #3


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    Traffic jams act like waves propagating through the road network. One car brakes (for whatever reason) causing the car behind it to break and the car behind that to break etc etc. You can see a very clear representation of it with this simple model (I advise playing around with the density and letting it run to observe traffic jams developing). A jam couldn't take out an entire road network though, not unless an inconceivably high percentage of cars were all travelling to the same place. Traffic jams become less of a problem the less cars they are and the further back a traffic jam goes the more potential off-routes it will pass. So you'll get more and more cars turning off either because that's the route they need to take or because they're avoiding it.
  5. Nov 21, 2016 #4


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    Only if it doesn't brake...:smile:
  6. Nov 21, 2016 #5


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  7. Nov 21, 2016 #6


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    It happened. Big evacuations are an example.
    One interesting case was the total solar eclipse of 1999: The only one in Germany in the 20th century, and the only one in the 21st century will be 2081 - unless you want to take an airplane flight to hunt them, the 1999 one was a once-in-a-lifetime experience for many. Millions drove to Southern Germany to see it. And after the sun came back, millions wanted to get back at the same time. The north/south highways got traffic jams up to ~100 km length, the second-level streets (Bundesstraßen) got completely blocked quickly as well, and even some third-level streets got massive jams as people tried to avoid the jammed bigger roads.
  8. Nov 21, 2016 #7


    Staff: Mentor

    Whom do you tell ... it was awful. Everywhere!
  9. Nov 21, 2016 #8
    This is going back a while, but at one time I worked in London, which has a circular ring road (M25 motorway).
    Most of the time it does what it's there for, distributing incoming traffic to the part of the city they want, and providing hubs for outgoing traffic.
    When it messes up though due to an accident or something there can be complete chaos.
    The motorway itself is jammed, and nothing much can either get in or out of the city, gridlock inside and outside.
    It could take several hours for things to return to normal.
  10. Nov 21, 2016 #9


    Staff: Mentor

    "All road intersections will be replaced with roundabouts, and you will start driving on the left. At the same time, you will go metric without the benefit of conversion tables. Roundabouts and metrication will help you understand the British sense of humour." (John Cleese)
  11. Nov 30, 2016 #10


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    Not only in Germany! We were on the highway Balaton-Budapest at the time.
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