[fransje26]

> If you double following distance, you halve the throughput. If you halve following distance, you double your throughput.

That postulate breaks down as soon as you move away from a laminar traffic assumption and include distracted drivers, lane changes, and weather influences. Which is why the wave theory model is important to understand the propagation of perturbations and their effect on maximum throughput.

> The throughput of a (full, i.e. rush-hour) road has nothing to do with speeds of people driving, and everything to do with following distance.

And yet, in the limit case of a bumper-to-bumper situation (or, in fluid dynamics parlance, an incompressible flow), the variable determining the change in mass flow-rate is the velocity of the medium. Mimetically, we could also look at ants. To ease congestion in a bumper-to-bumper situation, they accelerate.

[CGMthrowaway]

YES to all! You're so close. Drivers do not accelerate in bumper-to-bumper the way ants do. They maintain a 2sec (or whatever they are trained) following time instead. Which therefore dictates velocity (car lengths per following time). Thus the limiter on flow-rate is actually following time!