I was also waiting in the video to see busier traffic simulations, but didn't see any. I suspect the model of keeping distance then breaks down completely and creates lots of congestion, ifnot collisions (if the road is full and you need to evade an oncoming vehicle...). On the upside, you use the whole road dynamically instead of only a fixed few lanes, that is a nice improvement.
I think you under-estimate the numbers of cars on the road.
I don't remember the exact throughput used for the video, but I think it was around 5500. On a equivalent road the minimum distance between two cars is about 2 seconds. That gives a throughput of 1800 cars per road per lane (3600/2). For two lanes (resembling the one used in the video) this would give a absolute maximum throughput of 3600 roads per hour.
Which means that our system, with about 5000 cars per hour, give a much higher throughput than the maximal on a standard highway.
All the details is in the thesis (link in the url, or https://highwayflocking.github.io/Flocking_for_Road_Traffic_...).
At the very least, I reckon the "yield to higher-priority traffic", "maintain distance from other vehicles", "maintain distance from road boundaries", and "drive forward" behaviors to be (relatively) easy for human drivers to implement, seeing as they do these things already (albeit with lanes as visual reference points), and do so even better with modern driving assistance technologies like blind spot indicators. Dynamic adjustment to asymmetric load would be harder, but I suspect even this could be feasible.
I mean, if we are using AI to drive cars might as well use the most efficient configuration (and not one that only interacts with local neighbors as is required for fish).
Dynamic lanes seem useful though (if a bit scary).
In any case, typical interstate highways certainly have numerous interchanges, which are the other kind of junction.
I found this quote from it at the following link:
"Tall, ugly buildings loomed above them to shoulder out the sky. The black streets were wide but very crowded, and the Moties drove like maniacs. Tiny vehicles passed each other in intricate curved paths with centimeters of clearance. The traffic was not quite silent. There was a steady low hum that might have been all the hundreds of motors sounding together, and sometimes a stream of high-pitched gibberish that might have been cursing.
Once the humans were able to stop wincing away from each potential collision…"
Does that mean "If you have most of the cars going one way it's more efficient to use more of the road for traffic moving in that direction"? It sounds like it does. And, well, duh.