Zipper Merge News

[jeffandnicole]

Bullshit.  As soon as we're past the merge point around here, traffic speeds up.  The merge point IS the blockage point around Chicago.

Seconded. Anytime I've gone thru the Zoo Interchange construction zone zipper, traffic has sped up once we were out of the zipper.

So you guys go thru the merge zone 24 hours a day?  You guys have the vision of seeing conditions that exist at all times.

The only bullshit I see is that you're making numerous assumptions about traffic everywhere across the world.  What you need to do is sit above the construction zone to watch the entire thing develop.   "I went thru there on a Wednesday 3 weeks ago" doesn't qualify as knowing how these backups work.   All it takes is 86 year old Granny Thompson to drive 25 mph thru that construction zone 15 minutes ago to bottleneck everything up.

[jemacedo9]

I don't think there is any question around what to do when traffic is light:  merge over as soon as possible. But there is no adverse impact to when you merge, as long as you're not cutting someone off in the process at the last minute.  Besides the etiquette, that tends to slow down that person.

The arguments seems to be over what to do when traffic is heavy.  To that, here is the question:  is there any benefit to leave the closed lane empty by suggesting that the majority of people merge over early?  Om heavy traffic, a jam is going to exist whether everyone merges at the merge point, or if the majority of people merge early.

To me, the ideal situation is in heavy traffic everyone uses all lanes to the merge point, and then alternate. BUT...that only works if everyone alternates.  The second one person jumps their turn, this breaks down...but I don't see how the early merge solves this either.  Merging earlier might improve throughput at the merge point, but is negatively impacted at the earlier merge point.

Short answer:  is one really significantly better than the other?  Or are both no wins...when you factor in actual driver behavior? 

[DaBigE]

Bullshit.  As soon as we're past the merge point around here, traffic speeds up.  The merge point IS the blockage point around Chicago.

Seconded. Anytime I've gone thru the Zoo Interchange construction zone zipper, traffic has sped up once we were out of the zipper.

So you guys go thru the merge zone 24 hours a day?  You guys have the vision of seeing conditions that exist at all times.

The only bullshit I see is that you're making numerous assumptions about traffic everywhere across the world.  What you need to do is sit above the construction zone to watch the entire thing develop.   "I went thru there on a Wednesday 3 weeks ago" doesn't qualify as knowing how these backups work.   All it takes is 86 year old Granny Thompson to drive 25 mph thru that construction zone 15 minutes ago to bottleneck everything up.

You don't have to go thru it 24 hours a day to figure it out. We know it. The regular drivers of the corridor know it. WisDOT knows it, otherwise they wouldn't have put up all of the dynamic warning signs regarding stopped/congested traffic, UPSTREAM of the merge. Ever watch material travel thru a funnel? An hourglass? It speeds up past the point of narrowing. Just as jemacedo09 says, it's when traffic is heavy that the merge point becomes the issue. What traffic is doing at 2:30 am isn't the focus, because it doesn't matter where you merge with traffic being so light.

[kalvado]

Short answer:  is one really significantly better than the other?  Or are both no wins...when you factor in actual driver behavior?

My bet is that early merge is very slightly better in terms of throughput in case of light backups; but both are necessary evil, and both work equally... to the extent things can work - and both work  a little bit better when everyone is on the same page.
Late merge reduces/postpones propagation of backup into road access points, and as such may lead to slight increase of total wait time - assuming detours with ample capacity are available.

[jeffandnicole]

Bullshit.  As soon as we're past the merge point around here, traffic speeds up.  The merge point IS the blockage point around Chicago.

Seconded. Anytime I've gone thru the Zoo Interchange construction zone zipper, traffic has sped up once we were out of the zipper.

So you guys go thru the merge zone 24 hours a day?  You guys have the vision of seeing conditions that exist at all times.

The only bullshit I see is that you're making numerous assumptions about traffic everywhere across the world.  What you need to do is sit above the construction zone to watch the entire thing develop.   "I went thru there on a Wednesday 3 weeks ago" doesn't qualify as knowing how these backups work.   All it takes is 86 year old Granny Thompson to drive 25 mph thru that construction zone 15 minutes ago to bottleneck everything up.

You don't have to go thru it 24 hours a day to figure it out. We know it. The regular drivers of the corridor know it. WisDOT knows it, otherwise they wouldn't have put up all of the dynamic warning signs regarding stopped/congested traffic, UPSTREAM of the merge. Ever watch material travel thru a funnel? An hourglass? It speeds up past the point of narrowing. Just as jemacedo09 says, it's when traffic is heavy that the merge point becomes the issue. What traffic is doing at 2:30 am isn't the focus, because it doesn't matter where you merge with traffic being so light.

I've watched material go thru a funnel.  What happens if you stop that funnel for a minute while adding material to the funnel?  The material builds up without any way of getting it thru. 

In construction zones, the construction equipment has to enter and exit.  Those trucks aren't going to pull in and out at 55 mph.  They slow down.  Depending on the construction zone, they may even have to stop and back in to the work area, causing a total traffic stoppage.  That's the stuff that you don't see going on out there because you're not one of those cars within eyesight of seeing it, but can mightly contribute to the delays.

[jakeroot]

Bullshit.  As soon as we're past the merge point around here, traffic speeds up.  The merge point IS the blockage point around Chicago.

Seconded. Anytime I've gone thru the Zoo Interchange construction zone zipper, traffic has sped up once we were out of the zipper.

But if traffic merges too quickly into one lane, it's going to slow down. Cars cannot all universally react to a merge. Most react by braking to create a safe following distance, but that creates a chain reaction of braking, inevitably creating another slowdown. A safe gap to you, may not be a safe gap to the car behind you.

Rather than have multiple merge points, with multiple reactionary braking points, it's better just to have one. Use all the available lane space.

[briantroutman]

Regardless of whether early merge or late merge provides the highest theoretical throughput, there's another issue that I haven't seen mentioned. You could call it "equality of misery" .

It's somewhat like the prisoner's dilemma. You can look it up on Wikipedia if you're unfamiliar. The general concept was used in a show on Game Show Network some years ago called Friend or Foe. On that show, a team of two people would work together to win a jackpot, and then after they won, the two team members would secretly vote "friend"  or "foe" –under the table so that the teammate couldn't see how they voted. If both voted "friend" , they'd split the jackpot evenly. If both voted "foe" , neither one of them would take home anything. However if one voted "friend"  and the other voted "foe" , the trusting friend would leave empty-handed while the cynical foe would get the whole jackpot to himself.

A lane of a hundred early mergers–who all want to be good people and do the right thing–are essentially voting "friend" . They've all thrown their antes into the pot in the hopes of splitting it evenly. But this jackpot creates a very attractive opportunity for a handful of foes to scurry up the empty lane and snatch the spoils laying out in plain view. This leads to people coloring the situation in moral overtones: us, good people in the early merge lane...and them: bad people butting in line. This can easily escalate to vigilanteism among the "good"  folks and elevated acts of douchebaggery among the "bad" .

Even if late merge doesn't lead to higher throughput, it at least defuses the emotional powder keg. No prick in a BMW can steal the jackpot because there is no jackpot–everyone in both lanes has been waiting roughly an equal length of time.

[kalvado]

Bullshit.  As soon as we're past the merge point around here, traffic speeds up.  The merge point IS the blockage point around Chicago.

Seconded. Anytime I've gone thru the Zoo Interchange construction zone zipper, traffic has sped up once we were out of the zipper.

But if traffic merges too quickly into one lane, it's going to slow down. Cars cannot all universally react to a merge. Most react by braking to create a safe following distance, but that creates a chain reaction of braking, inevitably creating another slowdown. A safe gap to you, may not be a safe gap to the car behind you.

Rather than have multiple merge points, with multiple reactionary braking points, it's better just to have one. Use all the available lane space.

That is basically the essence of it - before the obstacle speeds are higher and more real estate is available, leading to higher mobility of the cars. THat, among other things, means easy recovery of time lost in merge.
Once you're in the narrows, any delay means added delay for all the cars waiting.
So, what do you think would provide higher entrance rate into the narrows - pre-formed single lane, where all driver need is to maintain following distance to car in front - or last second lane change, where you have to keep an eye on at least 2 cars at the same time?
THat is small effect, maybe few %% of total throughput at most, though.

[vdeane]

I don't think there is any question around what to do when traffic is light:  merge over as soon as possible. But there is no adverse impact to when you merge, as long as you're not cutting someone off in the process at the last minute.  Besides the etiquette, that tends to slow down that person.

The arguments seems to be over what to do when traffic is heavy.  To that, here is the question:  is there any benefit to leave the closed lane empty by suggesting that the majority of people merge over early?  Om heavy traffic, a jam is going to exist whether everyone merges at the merge point, or if the majority of people merge early.

To me, the ideal situation is in heavy traffic everyone uses all lanes to the merge point, and then alternate. BUT...that only works if everyone alternates.  The second one person jumps their turn, this breaks down...but I don't see how the early merge solves this either.  Merging earlier might improve throughput at the merge point, but is negatively impacted at the earlier merge point.

Short answer:  is one really significantly better than the other?  Or are both no wins...when you factor in actual driver behavior? 

Exactly.  When traffic is light enough that there are still gaps, if everyone merges into a gap at a speed such that they don't force traffic behind them to slow down, it significantly reduces the chance of a backup.  The majority of backups I've ever been in have been caused by people messing this up, usually by cutting into a lane slower than traffic is moving in that lane without a sufficient gap to accelerate before the car behind then needs to slow down.

When traffic is heavy, of course, everyone should do a zipper merge at the same place.  Ideally that would be at the end of the lane rather than some random point, but I would rather everyone do a zipper merge all at the same point rather than most do it at one point and a few people heading down the rest of the lane, jumping the queue while forcing everyone else to stop to let them in instead of accelerate back up to speed.  The latter situation happens ALL THE TIME with my commute (in summer) with a couple acceleration lanes and it's EXTREMELY frustrating.

[kphoger]

But changing lanes when there's no lane drop at point A versus changing lanes at point B a half-Mike farther back isn't necessarily better or worse. How does the presence of a lane drop make A better than B. Same action performed, same location, the only difference is the presence of road cones in a portion of the roadway not even being considered.

[corco]

I guess to me there's a really simple solution to this:

1. If it is possible to change lanes before the merge point without coming to a complete stop or near complete stop and forcing your way in (causing vehicles in the adjacent lane to obviously need to brake) to do so, change lanes as soon as possible.

2. If it is impossible to change lanes before the merge point without coming to a complete stop or near complete stop and forcing your way in (causing vehicles in the adjacent lane to obviously need to brake) to do so, change lanes at the final merge point.

In practice, what this means is that you don't change lanes if it's going to require the car behind you to brake (in your own judgment), and as soon as you see a suitable gap, you should change lanes. If that is impossible, you will be forced to change lanes at the merge point, and there's nothing wrong with that.

I don't see why that is so complicated. There's no one-size-fits all solution. If traffic is flowing well, there's no point in impeding it by changing lanes at the final merge point. If traffic is moving slowly, just use the maximum amount of lane capacity and change lanes at the merge point. What's stupid is seeing somebody 200 feet before the merge stopped in a lane trying to wedge their way into the adjacent lane, holding everybody else up behind them. That person isn't driving correctly and is just adding a level of complexity to navigating traffic.  The actual merge point provides a visual cue to drivers in the continuing lane that they need to slow down to let cars in, whereas it's easy to blow by some poor sap sitting stopped in a non-ending lane with their turn signal on. That's where collisions happen. 

[1995hoo]

"The agreed upon merge location"? Says who? I see NO agreement on the roads, period. People get over at all sorts of different points and then they all seem to say, in essence, "Thou shall not use this lane past this point because I said so."

[kalvado]

"The agreed upon merge location"? Says who? I see NO agreement on the roads, period. People get over at all sorts of different points and then they all seem to say, in essence, "Thou shall not use this lane past this point because I said so."

So you are that asshole, who drives in an empty lane past patiently waiting cars and demands an entry at the head of the queue?

[Rothman]

"The agreed upon merge location"? Says who? I see NO agreement on the roads, period. People get over at all sorts of different points and then they all seem to say, in essence, "Thou shall not use this lane past this point because I said so."

So you are that asshole, who drives in an empty lane past patiently waiting cars and demands an entry at the head of the queue?

No, he's the smart one using the full capacity of the road like everyone else should be doing.

[kalvado]

"The agreed upon merge location"? Says who? I see NO agreement on the roads, period. People get over at all sorts of different points and then they all seem to say, in essence, "Thou shall not use this lane past this point because I said so."

So you are that asshole, who drives in an empty lane past patiently waiting cars and demands an entry at the head of the queue?

No, he's the smart one using the full capacity of the road like everyone else should be doing.

I was also one of those kids who loved to use full capacity of the room by spreading things uniformly across entire floor...
But I don't understand what "full capacity" means in terms of highway usage. Is that the same as touching base on synergy to leverage joint efforts into meeting deliverable milestones?

[Rothman]

"The agreed upon merge location"? Says who? I see NO agreement on the roads, period. People get over at all sorts of different points and then they all seem to say, in essence, "Thou shall not use this lane past this point because I said so."

So you are that asshole, who drives in an empty lane past patiently waiting cars and demands an entry at the head of the queue?

No, he's the smart one using the full capacity of the road like everyone else should be doing.

I was also one of those kids who loved to use full capacity of the room by spreading things uniformly across entire floor...
But I don't understand what "full capacity" means in terms of highway usage. Is that the same as touching base on synergy to leverage joint efforts into meeting deliverable milestones?

No.

[jemacedo9]

PennDOT has signs in some work zones where they want to have a zipper merge...one stating "USE BOTH LANES TO MERGE POINT" and then at the merge point, "MERGE HERE - TAKE YOUR TURN".  THIS would clear things up quite nicely if used more widespread where engineers determined a zipper merge should be used.

[kalvado]

"The agreed upon merge location"? Says who? I see NO agreement on the roads, period. People get over at all sorts of different points and then they all seem to say, in essence, "Thou shall not use this lane past this point because I said so."

So you are that asshole, who drives in an empty lane past patiently waiting cars and demands an entry at the head of the queue?

No, he's the smart one using the full capacity of the road like everyone else should be doing.

I was also one of those kids who loved to use full capacity of the room by spreading things uniformly across entire floor...
But I don't understand what "full capacity" means in terms of highway usage. Is that the same as touching base on synergy to leverage joint efforts into meeting deliverable milestones?

No.

But it is equally meaningless.
I mean "full capacity" in this situation does not translate into anything meaningful.
Travel times are not reduced
Safety is not improved.
Maintenance costs do rot reduce.
Nothing.

This is just another piece of managementspeak.

Feel free to explain why I am wrong, but try to be technical, no bullshit please.

[kalvado]

If the volume exceeds the capacity for a single lane, jamming and delays will occur in the continuing lane as people try to change out of the terminating lane--in this case, early merging would only worsen the jam (case 2 as described above).

Wrong.

[paulthemapguy]

If the volume exceeds the capacity for a single lane, jamming and delays will occur in the continuing lane as people try to change out of the terminating lane--in this case, early merging would only worsen the jam (case 2 as described above).

Wrong.

Excellent refutation 10/10       

[1995hoo]

If the volume exceeds the capacity for a single lane, jamming and delays will occur in the continuing lane as people try to change out of the terminating lane--in this case, early merging would only worsen the jam (case 2 as described above).

Wrong.

Excellent refutation 10/10       

Yup. Between that and calling people "assholes" and the like, I wonder if he's someone else in disguise. No matter. I don't see much point wasting time answering that sort of nonsense, so I think I'm done with this thread. He can do whatever he wants.

[kalvado]

If the volume exceeds the capacity for a single lane, jamming and delays will occur in the continuing lane as people try to change out of the terminating lane--in this case, early merging would only worsen the jam (case 2 as described above).

Wrong.

Excellent refutation 10/10       

I wrote full explanation at least twice before. Try looking things up on a previous page. 

[vdeane]

Again, speed differential while merging is the culprit.  Once everyone has actually merged, braked, adjusted following distance, etc., then things can get back to somewhat-normal.  I remain unconvinced that exactly where than merging happens is all that important, which is why some states are jumping on the zipper merge (Kansas) and some states have big orange signs saying <-- STATE LAW MERGE NOW (Oklahoma) a mile in advance.  There's no obvious benefit to either one.

Exactly.  If there's space to merge into a gap without affecting traffic, do so.  If not, have everyone do a zipper merge.  The end of the lane would be the most logical place, but if everyone's doing it elsewhere, don't be the guy butting in down the road.

[paulthemapguy]

If the volume exceeds the capacity for a single lane, jamming and delays will occur in the continuing lane as people try to change out of the terminating lane--in this case, early merging would only worsen the jam (case 2 as described above).

Wrong.

Excellent refutation 10/10       

I wrote full explanation at least twice before. Try looking things up on a previous page.

And ya still didn't learn anything.  From me, from jake, from any of the people who have made pretty much the same point as I did.  So we'll just agree to disagree I guess.

And vdeane summed up the general conclusion pretty well in the post above.

[kalvado]

If the volume exceeds the capacity for a single lane, jamming and delays will occur in the continuing lane as people try to change out of the terminating lane--in this case, early merging would only worsen the jam (case 2 as described above).

Wrong.

Excellent refutation 10/10       

I wrote full explanation at least twice before. Try looking things up on a previous page.

And ya still didn't learn anything.  From me, from jake, from any of the people who have made pretty much the same point as I did.  So we'll just agree to disagree I guess.

And vdeane summed up the general conclusion pretty well in the post above.

Well, point is that zipper merge elsewhere, as vdeane called it, is effectively an early merge. As long as you agree that is an equally good (or bad - since there is no truly good option here) alternative, we're on the same page.