This is incorrect because your creating an extra long line that isn't needed and not utilzing that 2nd lane.
That's not relevant. The problem is more an issue of merge conflicts than traffic volume per lane. So the remedy is to eliminate the merge conflicts by having the merges take place where traffic is flowing freely and everybody is traveling at highway speed. If everybody traveled at the posted limit for the construction zone, it wouldn't matter if there was only one line.
Then if you happen to be in a city and there is a stop light,
(snip)
Nobody's talking about local roads here.
The most efficient way is to utilize the two lanes to the max and have cars alternate.
You would think so, wouldn't you? HOWEVER, that's only if machines are driving the cars. If you were running a simulation with a computer controlling the blips that represent vehicles, it would definitely work that way. But that's not taking human nature and human fallibility into consideration.
You have to consider Widow Blinkenheimer, whose husband used to drive her wherever she needed to go. Well, he passed on, and Widow Blinkenheimer, she doesn't see too good, and her reflexes and judgment, well...
You have to consider Tiffany, who doesn't have a lot of driving experience to begin with, and she just broke up with her boyfriend because he's a cheating louse and asked that

Michaela to the prom, so she's angry and upset and trying to text all her friends about it, and she's also thinking about her biology test tomorrow, and what's this zipper thing up here? What did that sign say?
You have to consider that some percentage of jacktards are always going to feel the need and the right to get ahead of just a couple more cars...
And you have to remember that zipping like you're suggesting will naturally create congestion. People will do it slow. Not construction zone slow, but slower, and that's when you see backups for miles. Throw an accident into the mix in the zipper zone because everybody's merging at once, and now the real fun begins!
I'm sure your idea works fine in simulations, but once you factor in the human element, it doesn't work I'm practice for more than a few minutes before it gets FUBAR.
I was in the men's room at a Pilot one day, and one driver was wiping down the counter. I commented on the futility of his endeavor. "It's just going to be all wet again in 5 minutes," I told him.
"Oh, I dunno...if we all just take an extra minute to be careful to not splash water around and clean up after ourselves..."
Call him an optimist, I guess. Again, if we were machines, that would work, but factor in the human element, and it goes out the window. He saw things how they COULD be under ideal circumstances, and I viewed things how they ARE. Same thing here.
Being safe and merging early is a sacrifice that big truck drivers choose to make. That doesn't mean they should screw everything up for everyone else because they don't have the mobility that small cars do.
No, merging early is something professional drivers do because they see human nature in action behind the wheel all day, and most are more realistic than to expect the zipper plan to work, and realize that a better plan is to get everybody in one line while at highway speed while there's plenty of room on the highway, then go through the construction zone at the posted speed. As long as the merges happen before the slowdown, there would be NO BACKUPS.