Except unlike prisoner's dilemma, it's not a zero (or negative) sum game. The entire traffic flow can speed up if zipper merging is done. The "late mergers" don't have to risk losing their game of "chicken" while the "vigilantes" don't have to deal with the reckless maneuvers of some of the former.

People don't do zipper merging because people are human and drive emotionally [1]. The stereotypes of the conservative early merger claiming the moral high ground and the reckless late merger doing anything to save a few minutes are the cultural results of this mentality.

[1] Another example is the special breed of driver who stops the traffic flow on a major road (which has the right of way) to let someone on a minor cross road or parking lot exit onto the major road, thus inconveniencing everyone behind them for the self satisfaction of having helped the one person they can see.

1. The same thing applies to stopping to let people turn left across traffic, where the left lane of oncoming traffic is stopped and the right lane is clear.

This is similar to the person on a grocery checkout line who lets someone cut in front of them; they are also putting that person ahead of every other person behind them the line.

It's an interesting situation; people feel they are doing the right thing yet apparently never stop to think how they are imposing their decision on others.

There's a blind-spot of sorts regarding the larger effects of their actions.

Or because you know that otherwise they'll be at that crossing for the next hour if nobody's willing to let them by. Perhaps there are some funny allusions to net neutrality to be made here...

The scenario I had in mind while writing my post is that of the local road which crosses a major stretch of highway. Such highways might be an actual interstate, a busy two-lane highway, etc. One of the worst types of road to cross is the one that is far too wide for its own good– an ambitious 6-lane road with not enough traffic to ever be full (Trenholm Road in SC, ahem), but enough so that drivers spread out across all lanes and make crossing very annoying sometimes. There are parts of the Taconic (NY) that pretty bad to cross, though I'm usually the one on the highway. The local cross sometimes gets backed up 5-10 cars, 2-3 of which are stuck in the median. Getting on the highway or going around by going the next town can add 10+ miles. Letting someone cross by slowing down a bit and changing lanes is not, in my opinion, a smug assault on the efficiency of those driving on the highway... it's just something a few people do when they recognize that nothing is very efficient anyway. (Note that I haven't said much about safety because it was only a small part of their comment, and not the part I was responding to. I hope it's clear that I am not advocating for people to test fate by slamming their brakes to let someone curtsy across the pavement.)

If everyone knew about zipper merging there would be no early mergers (and 'late mergers' don't exist within the context of zipper merging).

The real problem is accountability. There is none of it(as cops can't be everywhere, all the time) so people end up exercising what little power they do have in order to punish those they view as the abusers.

I may be overly optimistic, but I think a sign saying "use both lanes and zipper merge at end" would do a lot.

However, educating people does allow them to make better decisions.

Rules themselves aren't always the best/optimal/safest solution either and being loose may be the best solution.

For example, in one country in Asia if you are "in-front" of someone you have the right to merge/enter a roadway/get on a free way/change lanes over the person already in the lane. This is just cultural and is so much better than what we have in the west (like the USA). If someone changes lanes and "hits you", it is your fault (unless you were in-front of them).

Makes it so much easier to get on the free way, change lanes, etc. as you only have to worry about what is in front of you. Not what is in front of you, behind you, next to you, etc. There are no "blind spots" etc.

Obviously when you're going 100 km/h, the ideal merge point is significantly farther back than when it's stop and go. Nobody is saying you should wait until you're 20 feet from the barrier and then swerve into the other lane. But it's not like that's unique to this situation.

If you move the merge point back, then by definition it becomes an early merge, right? I don't understand your disagreement with what seems like a totally reasonable statement by Justin.

If you define "late" as "the latest point at which you can safely merge without causing negative traffic reactions (e.g. by forcing someone to brake)" then zipper/late merging is better than "moving over as soon as you can", even in light traffic.

I agree. But note that the idea of Zipper merging is when traffic has already slowed down, not when it is still moving.

It is optimal only when the local driving culture allows it to be.

I live in an area where drivers are extremely selfish and the police don't seem to spend a lot of time ticketing bad drivers, so zipper merging typically doesn't work here.

This is backwards. Zipper merging doesn't work when drivers attempt to be unselfish by merging early, which results in vigilante lane blockage of those who weren't as considerate. In other words, I'm not being selfish when I block late mergers; I'm enacting justice on other people who were being selfish.

The system works when all parties recognize that the best thing for everyone is to merge late.

One of the reasons why people early merge here is that many people don't let mergers in. And one of the reasons why people don't let mergers in is that they regularly get cut off by a second car after letting a merger in. It's a vicious circle.

Back in "the day", zipper merging wasn't even an issue. A lot of people early merge here because they'd rather be the one letting people in than hoping to be let in.

Yeah, which is why almost the entire article was about the campaigns to change the culture, not about justifying zipper merging as optimal.

Those campaigns in Washington and Minnesota just wouldn't fly here.

When our metro population was around <=3M, people still zipper merged (in the mid 90s and earlier).

This is so true. At congested merge points in my city, you have people who don't really care about the alternating needed to make a zipper merge work. First, you have people who just won't let people in, and then you have people who will try to sneak into the lane with the merging car ahead of them.

In the same way one or two bad drivers can destroy a lane or two of functional traffic flow, a good driver can create a lane (or two) of harmony.

In Florida, we all have a non-verbal mutual agreement that we're all trying to screw each other out of the best spot in the road. We all want to be going faster than everyone else, we all want to get to the front of the line and skip all the chumps, we all want to move into the lane we think will move the fastest at a red light, and we all think turn signals will just warn someone when we're trying to get ahead so they can take our spot on the road.

It honestly wouldn't be so bad if we could keep the speeding and aggressive driving controlled, but there's an unusual number of highways with ridiculously reduced speed limits (55mph on I-95 in Miami, I shit you not.... right around a large stretch of road where 45mph is the minimum speed limit) and a lot of assholes who think they're more important than everyone else. Not much you can do about it, other than a "fast lane", which is basically what they've created for a large stretch of I-95 combined with the Sunpass system.

They are screwing up the system by merging too early, then adding insult to injury, getting all bent out of shape about people who aren't 'early mergers'.

So first they create the problem, then they get upset when someone does it the right way. Classic!