The concept isn't new: planes have been landed automatically based on radio waves of the ILS system. But compared to a landing procedure on a single runway in a controlled space with necessary ground equipment to aid in the process, car traffic is not so much static.

The automatic following system will bump into fundamentals and the close proximity of the participating cars will only magnify their effect.

Consider a ten car "train" (or convoy) following the first car automatically. Their speed is higher than usual and they drive within a few meters of each other, all carefully controlled by a computer. Then the first car hits a big elk (moose).

The weight of the animal itself is sufficient to cause a significant, sudden decrease in the speed of the car body. While the sensors on the second car do notice that the first car slowed down (due to the impact), it cannot possibly brake to a stop without hitting the first car. If the convoy is driving 100 km/h no car is going to stop in time if the forecar loses a significant percentage of its speed in a short flash.

Now, what happened between the first and the second car will continue to propagate far back in the convoy and the end result is a pile of ten cars mostly crushed into each other.

Maybe there are no elk on a highway. Make it someone who had learned his driving skills on a Russian highway (you must have seen the Youtube videos). Or someone's tire blows up and that car spins to the adjacent lane straight in front of the first car.

But there's a good reason to have a speed-dependent 2-4 second safety margin between cars, and robotic controls and computerised radio links aren't going to change the physics.