There's a limited tolerance/buffer (a literal buffer: the distance cars keep between themselves) for the compression waves caused by humans "overbraking". Once

There's a limited tolerance/buffer (a literal buffer: the distance cars keep between themselves) for the compression waves caused by humans "overbraking". Once the buffer is gone, the whole system dramatically collapses to stop-go traffic jam. It's why (theoretically) automated highway driving can increase the car throughput: they can gain foreknowledge and better "system planning" via mesh communication and consensus (they are motivated because without consensus the system crashes to traffic jam), and probably/possibly follow each other much more closely to maximize the use of the concrete geography.