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Author Topic: Interdependent Delays  (Read 439 times)

webny99

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Interdependent Delays
« on: May 29, 2019, 01:49:02 PM »

This might sound like an unusual thread title, but allow me to explain:

The most obvious example would be when traffic on a freeway backs up (during rush hour or a one-off event like an accident), causing backups on parallel local streets. The delays on the local street will only be sustained so long as the freeway remains congested.

But what about two backups on the same road where the second one is dependent on the first, i.e. the first backup feeds the second one. This happens every afternoon on a two-lane road near me. The first backup is a major bottleneck, due to two lanes merging into one. There is also another major constraint about a mile downstream at an overcapacitated traffic light, where turn lanes are badly needed and delays on all four approaches are common. The interesting thing is that the stoplight cannot create a major backup on its own unless the lane merge backs up first. As soon as that happens, you can guarantee that volumes will soon start hitting the stoplight at an unsustainable rate, and traffic will start reverberating from the stoplight to such an extent that the two delays will become one and the same, and there will be a mile long wall of stopped traffic. As soon as the backup at the lane merge clears, within minutes so does the backup at the stoplight.

What other examples of this exist? For this thread it would need to be something recurring, not just a fluke or a one-off event.
« Last Edit: June 03, 2019, 08:45:13 PM by webny99 »
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thspfc

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Re: Interdependent Traffic Jams
« Reply #1 on: May 29, 2019, 05:23:02 PM »

Maybe Verona Road and the Beltline in Madison? Though not the same blacktop, they are the same route (US-18), and Verona Road is usually not backed up (except at McKee where it's always backed up no matter what), unless the Beltine is. Not a great example, but a start.
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planxtymcgillicuddy

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Re: Interdependent Traffic Jams
« Reply #2 on: May 29, 2019, 08:53:43 PM »

I feel like this happens somewhere in Boone, NC every day, especially inside the App State campus, and with those super-long redlights they have. I once stopped four times in the same redlight in Boone before finally getting to the end of it.
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webny99

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Re: Interdependent Delays
« Reply #3 on: June 03, 2019, 08:42:11 PM »

I probably didn't explain myself very well, but I think those are both good examples, and I'm sure there's many more.


I once stopped four times in the same redlight in Boone before finally getting to the end of it.

My way of expressing that would be "It took four waves to clear the stoplight". No one else I know uses "wave" in the context of traffic; I guess I'm not sure where I picked it up.
« Last Edit: June 03, 2019, 08:51:41 PM by webny99 »
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roadfro

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Re: Interdependent Delays
« Reply #4 on: June 11, 2019, 03:22:16 AM »



I probably didn't explain myself very well, but I think those are both good examples, and I'm sure there's many more.


I once stopped four times in the same redlight in Boone before finally getting to the end of it.

My way of expressing that would be "It took four waves to clear the stoplight". No one else I know uses "wave" in the context of traffic; I guess I'm not sure where I picked it up.

'Cycle' would be the proper traffic signal terminology in that context. As in, "it took four cycles for me to get through that signal."

'Wave' is a term more closely associated with a 'green wave', which is the ability for a platoon of vehicles to pass through multiple green signals in a row along a well-timed coordinated corridor.
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webny99

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Re: Interdependent Delays
« Reply #5 on: June 11, 2019, 08:35:22 AM »

I once stopped four times in the same redlight in Boone before finally getting to the end of it.
My way of expressing that would be "It took four waves to clear the stoplight". No one else I know uses "wave" in the context of traffic; I guess I'm not sure where I picked it up.

'Cycle' would be the proper traffic signal terminology in that context. As in, "it took four cycles for me to get through that signal."

'Wave' is a term more closely associated with a 'green wave', which is the ability for a platoon of vehicles to pass through multiple green signals in a row along a well-timed coordinated corridor.

Yeah, I guess I knew that 'cycle' would be the correct term.

I think in this case my use of 'wave' stems from the fact that the signals on this corridor are indeed timed perfectly. The problem is that "perfect" is simply not enough for the traffic volumes being handled here. Thus, the green wave fails; the backup at the lane merge is too long, and 10+ cars at the end of the line must stop for the next red light. So the next batch of cars, starting off from the previous light, hit stopped traffic instead of a clear green light, ensuring the same thing will happen at the end of the next cycle, and so it continues. The way I see it, the timing hasn't changed; the green waves are still occurring, but the traffic isn't benefiting from them. Instead, the stream ends up moving so slowly that traffic that was supposed to get through on one green wave might not get through until two or three more waves of greens have passed, i.e. traffic is progressing at a much slower rate than the light cycles.
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