  We have revealed physical features of autonomous driving in the framework of
the three-phase traffic theory for which there is no fixed time headway to the
preceding vehicle. A comparison with the classical model approach to autonomous
driving for which an autonomous driving vehicle tries to reach a fixed (desired
or "optimal") time headway to the preceding vehicle has been made. It turns out
that autonomous driving in the framework of the three-phase traffic theory
exhibits the following advantages in comparison with the classical model of
autonomous driving: (i) The absence of string instability. (ii) Considerably
smaller speed disturbances at road bottlenecks. (iii) Autonomous driving
vehicles based on the three-phase theory decrease the probability of traffic
breakdown at the bottleneck in mixed traffic flow consisting of human driving
and autonomous driving vehicles; on the contrary, even a single autonomous
driving vehicle based on the classical approach can provoke traffic breakdown
at the bottleneck in mixed traffic flow.
