[jmcdiesel]

There are non-rational things like animals, kids, and adults with their face in their phones to watch for, so it will never be fully rational...

However, the fact that the computer in the following car can detect instantly that the front car is slowing, it can react instantaneously and (theoretically, with similar braking distances) the following car would stop exactly the same distance (give or take a few inches) from the leading vehicle as when they were driving at speed...

[crucini]

OK, so we agree that the lead auto-car may still apply maximum braking unexpectedly. Therefore the follower needs to leave enough space to compensate for reaction latency, difference in braking power, etc.

So how does data communication (or lack thereof) affect this?

The follower can instantly detect that the leader is slowing via sonar/lidar/radar, right?

[jmcdiesel]

Seems like it would be near instantaneous, right? As soon as the leader brakes, the brake lights would be on (speed of light essentially) ... the following car would recognize that, along with radar/lidar type technology. I would imagine the reaction time would be nearly instant...

Then the distance between the cars that they should hold should be calculable by enforcing braking performance on the automated cars...

Assuming its enough, a simple 2 carlength rule would 1) give enough distance to stop and 2) allow for merging easily (second car would slot into place, following cars would slow slightly to make the gap again) ...