That's because you're thinking of human drivers whom are so slow to react that it is recommended they keep a whopping 2 or 3 seconds [0] worth of trailing dista

That's because you're thinking of human drivers whom are so slow to react that it is recommended they keep a whopping 2 or 3 seconds [0] worth of trailing distance to respond to changing road conditions like the person in front of you slamming on their breaks. The hypothetical clustering of self driving cars requires them to react at much faster times so they don't need to keep as much space between them. [0]: https://en.wikipedia.org/wiki/Two-second_rule https://en.wikipedia.org/wiki/Two-second_rule