>

You raise a good point, but I also don’t see cops writing tickets to people who merge like jerks. So it seems that the system being designed for maximum conflict doesn’t actually get utilized. So to answer your question, “efficient” would mean the greatest number of vehicles able to pass a merge point in the shortest amount of time.
/u/I_play_trombone_AMA (OP) has awarded 1 delta(s) in this post.
All comments that earned deltas (from OP or other users) are listed here, in /r/DeltaLog.
Please note that a change of view doesn't necessarily mean a reversal, or that the conversation has ended.
^Delta System Explained ^| ^Deltaboards >

Who has the right of way in that situation?
The reason some people think they are in the “right” lane is because they are. The drivers entering the “right” lane are legally responsible for yielding. There is no legal responsibility to let anyone in, ever. It just doesn’t exist.
Zipper merging is more of a social norm where people take a “treat others the way you’d want to be treated”. >

You’re proving my point. Zipper merges shouldn’t be a “social norm.” They should be part of the traffic code, which I believe will lead to safer and more efficient traffic flow. 
The way you’ve described it here is exactly how people are conditioned to think based on current signage and paint markings. My view is that if we changed the signs and paint, traffic would be safer and more efficient. 
In my ideal design, neither lane would have “right of way”. They both need to make sure the space is clear to merge. If an accident happened, the default result should be that both drivers would share fault for not ensuring the space was free to merge. Obviously if there are witnesses saying that one driver was driving aggressively, or the front of one car hit the back of the other car, then that could outweigh the default assumption of 50/50 liability. >

Then the issue isn’t the signage. Your issue is with the actual laws. Changing a sign isn’t changing a law. The painting/signs has nothing to do with it. >

The paint and signs do have something to do with it. The paint and signs express the law simply so people can see it in the moment. So my assumption is that if the signs changed, the highway code would also have changed first to necessitate the change in signs.
I guess I’ll reluctantly offer a !delta because you got me on a technicality. I can see that your point about the law needing to change could also help with things like teaching the proper technique in drivers’ ed, or other driving instruction. If the law changed, education could change as well, which would lead to an improvement in the situation. 
So while you expanded my view, and that deserves a delta, I still think my proposed way of merging is superior to the one we currently use in America. >

Confirmed: 1 delta awarded to /u/BIGFATLOAD6969 (1∆).
^Delta System Explained ^| ^Deltaboards >

I'm a little perplexed what situation  you're talking about here. 
I've literally never seen these signs except when there really is an actual continuing lane and an actual ending lane. They don't put them on onramps where two lanes merge into 1 before reaching the interstate. 
This is a real sign, that's actually used in a situation where there isn't a continuing vs. ending lane. >


The signs should show two lanes (left and right), merging together into one lane (center).

While I don't think this solution would actually change anything, it doesn't seem to be even proposing a solution for anything except a situation where a 2 lane road turns into a one lane road.  How does this situation work if you're going from 4 lanes down to 3?  Or 3 down to 2?
On top of that, the current sign is designed as it is because one driver needs to have the clear, legal right of way.  With the signs as-is, that is the driving in the continuing lane.  If two cars collide while merging, it is clear who is at fault:  The driver who merged into a lane when it was not safe to complete that merge.
But if both drivers are given equal legal right to a lane as you propose, who has the right-of-way?  When two cars inevitably collide, who is at fault and who violated a traffic law?  It would seem that neither of them did, as per the signage, both of them had exactly equal legal right to the space they both possessed simultaneously. >

Take a look at this crudely drawn diagram.
The left image is how it currently is. The right image is my idea. It’s exactly the same as my proposed 2-lanes merging to 1-lane idea. You have the leftmost lane which is not involved in the merge, and then the two right lanes which merge down to a new single right lane. This scales to any number of lanes you could want. 
I addressed this in another comment, but I’m fine for both drivers to share 50/50 liability in the case of a collision. Both drivers failed to make sure the space was clear before merging. There could be extenuating circumstances that might place more than 50% liability on one party, but in the absence of that evidence, the default assumption should be 50/50. >


Take a look at this crudely drawn diagram.

Maybe this is part of the "crudely drawn" aspect, but this diagram is a LOT more than just a signage / paint change. Your image actually changes the shape and position of the roads themselves, in contrast to your assertion 

This entire problem could be solved by changing the signage and paint.

With the physical roads as they are, there's no way around the fact that one of the lanes physically goes straight and the other one ends, creating an asymmetry. If you want the two lanes to have symmetry, that necessitates a change to the geometry of the roads themselves, not just the signs/paint. >


This entire problem could be solved by changing the signage and paint.

How? Law as it is now does actually specify the "correct" and "incorrect" lanes - there is a lane that is continuing and a lane that is merging into and need wait unless they are let in. No changes of signage will change that, it would be even worse as people will assume that they are legally entitled to merge via zipper, only to cause a crash in which they will be at fault. 

This causes much larger lines and backups than would be necessary if people would do a zipper merge.

And causes less accidents. Zipper merge is great when people follow it, but it is a PITA when people are dumb idiots trying to forcibly merge. And one accident will create much bigger lines and backups.
What is more, how would you verify who is at fault if zipper merge would be required by law? You have two cars - one was following the continuing lane, second one was merging and hit the car in continuing lane. There are no indicators that show why that happened - it is as likely for continuing car to be a jackass and not let in merging car as likely for merging car to be a jackass who wanted to merge just behind a car that merged before them, before continuing car would close the gap.
So how are we to decide who is at fault in that situation? >


getting into the continuing lane much too early

Who decides what "much too early" is?
The problem is the dickheads who are behind you in the ending lane who zoom around you after you've merged into the continuing lane.  There's no reason anyone should ever let those jackasses merge into the continuing lane.
And no matter how late one waits to merge, there is always some jackass willing to go offroad to get around because they feel the person merged "way too early".
Simple:  If you are within eyesight of the sign indicating that your lane is ending, and the car in front of you moves to the continuing lane, you should move to the continuing lane without trying to get ahead of the car that has always been ahead of you.  Do that, and you've got the zipper merge you wan and no one being a jackass. >

If cars merge at a point besides when the lanes are actually merging, that’s not a zipper merge. This leads to road (the “ending lane”) being unused, and unnecessary backups. If a car can use the “ending lane” and zoom past everyone, that indicates that the improper merging technique has already caused a backup. >


If cars merge at a point besides when the lanes are actually merging

There is always room for one more car to zoom around you. >


You could change my view by showing evidence that the way I’ve suggested designing signs and paint for merges would somehow be less efficient or less safe, or by showing evidence that the way we currently do things is somehow a “feature, not a bug.”

Efficient to whom?  For the people who decide what rules to apply (by shaping the roads accordingly) or the people issuing citations and tickets, a lack of event causes a city budget shortfall.  They have incentives to make sure there is a maximum possible number of events which doesn't negatively affect them.  Even when it does, the cops can "selectively enforce" them.
Interstate doesn't have this problem because they don't cause (additional) budget shortfalls from a lack of events.  There is an incentive to keep it efficient because taxes from businesses rely on the interstate being uneventful.  This doesn't work with surface streets because the city usually collects more from tickets than from taxes from businesses.