Did you read the whole article? That's explicitly discussed, even with graphs!
> At low occupancy (cars per mile), drivers can go as fast as they’d like. As occupancy increases, so does flow rate, even though speed decreases somewhat due to everyone trying to maintain following distance. At a certain point, when occupancy becomes high enough, speed dips low enough to where drivers are unable to maintain their minimum following distance, and — catastrophe! — the flow rate decreases dramatically.
> At low occupancy (cars per mile), drivers can go as fast as they’d like. As occupancy increases, so does flow rate, even though speed decreases somewhat due to everyone trying to maintain following distance. At a certain point, when occupancy becomes high enough, speed dips low enough to where drivers are unable to maintain their minimum following distance, and — catastrophe! — the flow rate decreases dramatically.