5 ms·

Merging at the last possible moment _increases_ congestion. If there is a lane elimination, after the the lane has been eliminated, traffic speeds up, because t

by tmuir 13y ago

Merging at the last possible moment _increases_ congestion. If there is a lane elimination, after the the lane has been eliminated, traffic speeds up, because there is no remaining merging to complete. Thus, the earlier merging is completed, the sooner traffic can recover from the disruption. Also, spreading out the merges over a longer distance, versus everyone merging in the same spot allows traffic to recover from many small distributed disruptions instead of one centralized large disruption. Early merging = less traffic.

knowaveragejoe 13y ago
I've seen this in action even on a pretty long merge segment for a lane reduction. It's a feedback loop of sorts, lots of people zoom up attempting to merge at the last possible moment and bypass the line of people that are slowing down because people further ahead were zooming up and trying to merge at the last possible moment.
CanSpice 13y ago
Do you have any proof for this, or is it just baseless conjecture? I suspect the latter, because nearly every link when you search for "traffic merging studies" states that late merging is more effective at reducing congestion. From the Minnesota DOT: "Minnesota DOT engineers developed what they call a "zipper," which meshes cars quickly. Signs advise drivers of the upcoming lane closure, tell them to use both lanes up to a point and then direct them to take turns merging. When traffic is flowing, drivers merge early to avoid unsafe maneuvers. But when traffic is congested, motorists make full use of both lanes. The data revealed that the change reduced traffic lines by 35 percent and also brought down "lane changing conflicts," says Craig Mittelstadt, Minnesota DOT's work zone safety specialist." From the Virginia DOT: "The late merge should be considered for 2-to-1 lane closure configurations to improve throughput when large numbers of heavy vehicles are present (>20 percent) for the majority of the time and congestion and queuing are often present."
- saosebastiao 13y ago
  The Minnesota DOT website is widely cited by proponents of the zipper merge as a way of reducing congestion. However, it makes no claims about increasing throughput...it is about maximizing road space utilization. Early merges occupy more space, but the benefits to this space utilization are ancillary to the throughput congestion: fewer cross streets or exits are blocked by people not intending to use them. The question of lane change conflicts is not exactly clear...what is a conflict? When someone doesn't want to let you in? If so, that is a question of human behavior, not the physics of the situation. The Virginia site recommends late merges for when >20% of the vehicles are heavy vehicles, which is due to their merging complications (maybe something to do with those pesky "lane change conflicts"). It is obviously not a general recommendation. There is no clear data for either position on throughput...because ultimately throughput is limited by the bottleneck, which is the lane closure, not the merge behavior. People who spend too much time in their cars tend to be religious about the appropriateness of certain driving behaviors, and like any faith-based conviction, will tend to over-extrapolate empirical evidence to their context of choice.
- chiph 13y ago
  The "Zipper Rule" has been in effect in Germany for years. It's effective, mostly because everyone was taught it in driving school. No special signs needed - people just do it.
- tmuir 13y ago
  "Do you have any proof for this, or is it just baseless conjecture?" You mean, besides empirical evidence? Nope. I see it almost every day on my commute, which is riddled with construction. On the days that everyone merges well before the last possible moment, traffic moves at a quicker pace, because there is no one to cut you off, and my commute is shorter. On days that people decide to cut others off at the last moment, my commute is measurably longer. If you merge ahead of time, you are more likely to find an existing gap in traffic, which has little to no effect on the traffic's speed. Whereas, if you are merging at the last possible moment, you are necessitating a gap be created specifically for you, forcing others to slow down. If cars stay in the eliminated lane until the last moment, and then the speed of traffic increases after the bottle neck, it was the merging at the last possible moment that caused the slow down in the first place.
  - jedberg 13y ago
    And this is why traffic sucks -- because people prefer to rely on anecdote instead of hard scientific facts. The behavior you are observing is not zipper merging -- it's people being assholes and trying to skip traffic. If everyone merged at the last second it would move better.
    - tmuir 13y ago
      From Wikipedia: "Anecdotal evidence is an informal account of evidence in the form of an anecdote. The term is often used in contrast to scientific evidence, as evidence that cannot be investigated using the scientific method." I didn't say "this one time back in 2001". This is everyday for years. These are consistently observable data. Cars merge early, my commute is under 30 minutes. Cars merge late, and not just one or two (the north shore of chicago is chock full of entitled assholes), my commute is over 40 minutes. Sounds like a falsifiable hypothesis to me. One of the main reasons airplanes and trains are much safer than automobiles is that planes and trains have outside coordination of traffic, a third party who can see the bigger picture. Automobile traffic is thousands of individual actors who focus mainly on their own interests, and consider others around them only to avoid near term problems. Hoping everyone will magically act in concert, without government enforced obligation, is a pipe dream. Which is what the article points to, and proposes to solve with self driving cars. Self driving cars would allow the outside coordination that could facilitate zipper merging.
Systemic33 13y ago
The decrease in congestion is more likely to come from the sideeffects that incorrect merging brings. When you merge too early, you stretch out the queue, and this may slow down other traffic areas, like blocking an exit on the highway. By merging at last possible moment, more cars can be fitted in the same length of the queue. obviously traffic wont have higher throughput through this particular cause of queue, but the overall effect on the city is substantial.
fizz_and_buzz 13y ago
This is definitely untrue. There were a bunch of studies in Germany that concluded the opposite, which is why the laws were changed here. It is now often illegal to change lanes e.g. the last 300m before the merge point. There are several reasons: - The traffic jam is longer because less road is used and the traffic jam often reaches so far back into intersections that other roads get blocked that are unrelated to the actual blocked lane. - Several merge points slow down the traffic more often which create several waves of breaking and accelerating, instead of just one breaking instance.

by tmuir 13y ago

knowaveragejoe 13y ago

I've seen this in action even on a pretty long merge segment for a lane reduction. It's a feedback loop of sorts, lots of people zoom up attempting to merge at the last possible moment and bypass the line of people that are slowing down because people further ahead were zooming up and trying to merge at the last possible moment.

CanSpice 13y ago

Do you have any proof for this, or is it just baseless conjecture? I suspect the latter, because nearly every link when you search for "traffic merging studies" states that late merging is more effective at reducing congestion. From the Minnesota DOT: "Minnesota DOT engineers developed what they call a "zipper," which meshes cars quickly. Signs advise drivers of the upcoming lane closure, tell them to use both lanes up to a point and then direct them to take turns merging. When traffic is flowing, drivers merge early to avoid unsafe maneuvers. But when traffic is congested, motorists make full use of both lanes. The data revealed that the change reduced traffic lines by 35 percent and also brought down "lane changing conflicts," says Craig Mittelstadt, Minnesota DOT's work zone safety specialist." From the Virginia DOT: "The late merge should be considered for 2-to-1 lane closure configurations to improve throughput when large numbers of heavy vehicles are present (>20 percent) for the majority of the time and congestion and queuing are often present."

saosebastiao 13y ago
The Minnesota DOT website is widely cited by proponents of the zipper merge as a way of reducing congestion. However, it makes no claims about increasing throughput...it is about maximizing road space utilization. Early merges occupy more space, but the benefits to this space utilization are ancillary to the throughput congestion: fewer cross streets or exits are blocked by people not intending to use them. The question of lane change conflicts is not exactly clear...what is a conflict? When someone doesn't want to let you in? If so, that is a question of human behavior, not the physics of the situation. The Virginia site recommends late merges for when >20% of the vehicles are heavy vehicles, which is due to their merging complications (maybe something to do with those pesky "lane change conflicts"). It is obviously not a general recommendation. There is no clear data for either position on throughput...because ultimately throughput is limited by the bottleneck, which is the lane closure, not the merge behavior. People who spend too much time in their cars tend to be religious about the appropriateness of certain driving behaviors, and like any faith-based conviction, will tend to over-extrapolate empirical evidence to their context of choice.
chiph 13y ago
The "Zipper Rule" has been in effect in Germany for years. It's effective, mostly because everyone was taught it in driving school. No special signs needed - people just do it.
tmuir 13y ago
"Do you have any proof for this, or is it just baseless conjecture?" You mean, besides empirical evidence? Nope. I see it almost every day on my commute, which is riddled with construction. On the days that everyone merges well before the last possible moment, traffic moves at a quicker pace, because there is no one to cut you off, and my commute is shorter. On days that people decide to cut others off at the last moment, my commute is measurably longer. If you merge ahead of time, you are more likely to find an existing gap in traffic, which has little to no effect on the traffic's speed. Whereas, if you are merging at the last possible moment, you are necessitating a gap be created specifically for you, forcing others to slow down. If cars stay in the eliminated lane until the last moment, and then the speed of traffic increases after the bottle neck, it was the merging at the last possible moment that caused the slow down in the first place.
- jedberg 13y ago
  And this is why traffic sucks -- because people prefer to rely on anecdote instead of hard scientific facts. The behavior you are observing is not zipper merging -- it's people being assholes and trying to skip traffic. If everyone merged at the last second it would move better.
  - tmuir 13y ago
    From Wikipedia: "Anecdotal evidence is an informal account of evidence in the form of an anecdote. The term is often used in contrast to scientific evidence, as evidence that cannot be investigated using the scientific method." I didn't say "this one time back in 2001". This is everyday for years. These are consistently observable data. Cars merge early, my commute is under 30 minutes. Cars merge late, and not just one or two (the north shore of chicago is chock full of entitled assholes), my commute is over 40 minutes. Sounds like a falsifiable hypothesis to me. One of the main reasons airplanes and trains are much safer than automobiles is that planes and trains have outside coordination of traffic, a third party who can see the bigger picture. Automobile traffic is thousands of individual actors who focus mainly on their own interests, and consider others around them only to avoid near term problems. Hoping everyone will magically act in concert, without government enforced obligation, is a pipe dream. Which is what the article points to, and proposes to solve with self driving cars. Self driving cars would allow the outside coordination that could facilitate zipper merging.

Systemic33 13y ago

The decrease in congestion is more likely to come from the sideeffects that incorrect merging brings. When you merge too early, you stretch out the queue, and this may slow down other traffic areas, like blocking an exit on the highway. By merging at last possible moment, more cars can be fitted in the same length of the queue. obviously traffic wont have higher throughput through this particular cause of queue, but the overall effect on the city is substantial.

fizz_and_buzz 13y ago

This is definitely untrue. There were a bunch of studies in Germany that concluded the opposite, which is why the laws were changed here. It is now often illegal to change lanes e.g. the last 300m before the merge point. There are several reasons: - The traffic jam is longer because less road is used and the traffic jam often reaches so far back into intersections that other roads get blocked that are unrelated to the actual blocked lane. - Several merge points slow down the traffic more often which create several waves of breaking and accelerating, instead of just one breaking instance.