You could carry a near infinite amount of cars on a highway if you could instantly accelerate to near the speed of light!

In all seriousness, yes you’re right that there is a max throughput of people per hour even with ideal drivers and cars on a given highway. You simply do not have enough space.

The article was very interesting and informative, but that too assumes many ideal conditions. Re: zipper merging, the author really discounts the affect of confusion causing on cumulative delay. Of course that never letting anyone get in front of you, and decreasing your headway will theoretically let you get to your destination earlier, but you run the risk of needing to detour to an auto collision center. In a 2 to 1 merge, one of the lanes must delay themselves 2 more seconds, everybody playing chicken instead of sharing the delay across the two will cumulatively slow things down on the whole.

This can also be accomplished with a traffic volume sensor and a stop light on highway on-ramps.

This kind of traffic metering does already exist, as you’re probably aware!

But the fact that even just a single rail car holds 360 commuters, equivalent to 180 cars or more on the highway changes the math completely.