{"items": [{"author": "Danner", "source_link": "https://plus.google.com/114987071963782993407", "anchor": "gp-1328625796855", "service": "gp", "text": "The problem is that the 'last minute' merge has costly messaging time between the merging lane and the through lane, which causes the merger to slow down, and possibly stop completely, as they wait for a response to their signal and attempt to merge. this ripples up the line of cars, and moves the line into stop-and-go instead of a smooth zipper operation.\n
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\nhttp://www.youtube.com/watch?v=iGFqfTCL2fs\n is a solution, by a single person.", "timestamp": 1328625796}, {"author": "David German", "source_link": "https://plus.google.com/111229345142780712481", "anchor": "gp-1328625812555", "service": "gp", "text": "The typical construction signs give early notice of the lane closure, implying that people should act on it. I think we need additional signs instructing drivers to use a zipper merge. To really make the point, the middle line could also turn double-solid-white well before the lane closure is visible.", "timestamp": 1328625812}, {"author": "Andrew", "source_link": "https://www.facebook.com/jefftk/posts/206282186137681?comment_id=206293846136515", "anchor": "fb-206293846136515", "service": "fb", "text": "The same question can also be asked about situations on a contra dance floor and elsewhere. What can and should be done is a matter of ethics. Do we have a social contract? Categorical imperative? Do you cut into waiting lines? Do you eat all the cookies on the plate?", "timestamp": "1328626041"}, {"author": "Jeff Kaufman", "source_link": "https://www.facebook.com/jefftk/posts/206282186137681?comment_id=206295849469648", "anchor": "fb-206295849469648", "service": "fb", "text": "@Andrew: I don't understand your comment. It's not like eating all the cookies on the plate is somehow globally more efficient.", "timestamp": "1328626252"}, {"author": "David German", "source_link": "https://plus.google.com/111229345142780712481", "anchor": "gp-1328626295136", "service": "gp", "text": "Also, if I'm understanding this correctly, the zipper merge is only more efficient if both lanes are equally utilized up to the merge point. The occasional person cutting into the ending lane, passing some cars, and merging back in at the chokepoint has reduced efficiency on the margin, because of the signaling time \n@Danner\n describes.", "timestamp": 1328626295}, {"author": "Andrew", "source_link": "https://www.facebook.com/jefftk/posts/206282186137681?comment_id=206297279469505", "anchor": "fb-206297279469505", "service": "fb", "text": "Jeff, cutting into waiting lines or eating all the cookies is selfish, and has a negative global effect. I'm talking about a plate of cookies meant to be shared, not a plate of cookies that you cooked alone in your apartment.", "timestamp": "1328626395"}, {"author": "Jeff Kaufman", "source_link": "https://plus.google.com/103013777355236494008", "anchor": "gp-1328626512948", "service": "gp", "text": "@David German\n Some of the efficiency of using both lanes until the end is that the merge-jam is shorter. So it is less likely to block earlier exits and you have a shorter stretch of single-lane traffic.", "timestamp": 1328626512}, {"author": "Jeff Kaufman", "source_link": "https://www.facebook.com/jefftk/posts/206282186137681?comment_id=206299299469303", "anchor": "fb-206299299469303", "service": "fb", "text": "@Andrew: what I was talking about in the post is that it's actually better for everyone if drivers use both lanes up to the merge point: http://www.dot.state.mn.us/zippermerge/", "timestamp": "1328626613"}, {"author": "Andrew", "source_link": "https://www.facebook.com/jefftk/posts/206282186137681?comment_id=206306016135298", "anchor": "fb-206306016135298", "service": "fb", "text": "Jeff, ah yes, I see that a zipper merge is better in theory (when people agree to zipper), but it doesn't address the case of coming upon a long single line, which is common. I'm saying that cutting the long line is very selfish and not very beneficial.", "timestamp": "1328627473"}, {"author": "Andrew", "source_link": "https://www.facebook.com/jefftk/posts/206282186137681?comment_id=206318276134072", "anchor": "fb-206318276134072", "service": "fb", "text": "The zipper is sensible in the case of a 2-lane road merging to 1. You might as well \"fill the bottle\" to make efficient use of the space. But in the common case of a 4-lane highway with an exit line, I think a zipper is more dangerous and disruptive.
An additional problem is that you are asking drivers to have too much knowledge about the configuration of the bottleneck, and they are not likely to be able to make an optimal decision as a group, unless there are advisory road signs.", "timestamp": "1328628868"}, {"author": "Jeff Kaufman", "source_link": "https://www.facebook.com/jefftk/posts/206282186137681?comment_id=206324822800084", "anchor": "fb-206324822800084", "service": "fb", "text": "@Andrew: I wasn't thinking about exit lanes. That is different. I think the main difference is that most drivers are already in one lane and using both lanes would require separating and then merging again.", "timestamp": "1328629627"}, {"author": "David German", "source_link": "https://plus.google.com/111229345142780712481", "anchor": "gp-1328675982896", "service": "gp", "text": "@Jeff Kaufman\n Sure. The reality is that few people know why and how to zipper merge. (I didn't before today!) Therefore, a long stretch of single-lane traffic is inevitable. In that context, I still think that a few cars merging late just lengthen the line by making everyone else compensate for the unexpected. They also create those dangerously large differences in speed that \n@Lucas\n mentioned.", "timestamp": 1328675982}, {"author": "Andrew", "source_link": "https://www.facebook.com/jefftk/posts/206282186137681?comment_id=206744906091409", "anchor": "fb-206744906091409", "service": "fb", "text": "I think these articles are faulty, and the examples they use aren't analogous to merging traffic. I don't see how zipper is any safer than early merge. People will drive erratically when they don't have enough time to make a decision.
If you're going to set up a merge, set it up with enough prior notice so that people have the time they need. If you look at the photo example on the MNDOT web page, I can't envision a zipper merge making for better traffic flow out the far side of the merge than a long-single-line merge.
I also don't like the \"pouring rice\" example on the FHWA page.
In the case of auto traffic, we're trying to optimize the traffic flow rate. With pouring rice, once the rice is in the funnel, it moves due to gravity and flow rate through the pinch point. The rice kernels don't have a means of accelerating or adjusting flow rate with any intelligence. Cars do accelerate, and they will do so as much as is practical. The question of how fast people are comfortable driving as a function of the distance between cars is a different but related question.
Leaving gaps in dense traffic? I suppose you can enforce that with stop/go signals, but people aren't going to guess those gap rates with intuition. And you won't keep people from jumping into gaps unless you make it clear to people that it's not allowed, and you have enforcement of rules with some kind of surveillance.
There are enough variables here that it's just not clear to me that zipper merging is going to buy you anything. Yeah, I understand that these traffic engineers with their fancy queueing theory are insisting that it's better. I just don't see it.", "timestamp": "1328679980"}, {"author": "Jeff Kaufman", "source_link": "https://plus.google.com/103013777355236494008", "anchor": "gp-1328703753152", "service": "gp", "text": "@Lucas\n I think \"scenario 1\" from the link is pretty much what we're talking about. When people get mad at late mergers it's because they've been patiently waiting in a long line of stop and go traffic, no?", "timestamp": 1328703753}]}