It always comes to a point where the only way to improve traffic is to flatten the buildings people drive to, defeating the purpose.

Sometimes, you achieve good traffic flow by making a city so absurdly difficult to drive in that people give up, park in the outskirts, and take public transport.

Example: Amsterdam. In the city, there is almost no traffic, achieved through insanely twisty road signals, stupid expensive parking spots and no gas stations. And still, almost no traffic doesn’t mean no traffic… I can’t understand people still clinging to a car in such conditions.

The biggest issue with zipper merging is humans need to not be selfish for it to work.

The biggest issue is that humans need to be aware of all the cars around them. That means using side and rear mirrors, leaving appropriate space for larger vehicles, keeping track of your place in the line, and - also, yes, not being selfish.

Its very efficient when moving well

If you've ever been alongside a semi during a zipper merge, you'd know that's not true. Their visibility is limited and the vehicle is huge, so they have to move at a glacial pace to complete the merge. Then the people in the leading/trailing positions need to open up a much larger gap than with a traditional car, complicated by the fact that they may not know exactly how big the truck they're letting in is. And heaven help if there's something hanging off the back of the vehicle. That's scary, so it causes nervous drivers to try and get away from the rear of the larger vehicle, which further snarls the traffic.

Like, as a procedure executed by a machine with perfect information of all elements involved, its efficient. As a game theory exercise between individual drivers of different skill and temperament, riding in vehicles of varying sizes, on a road with obstructions and other potential hazards, it is decidedly not efficient.