  Evidence in the literature shows that automated and human driving modes
demonstrate different driving characteristics, i.e., headway policy, spacing
policy, reaction time, comfortable acceleration, and others. These differences
alter observed traffic dynamics and have an impact on energy consumption. This
paper assesses the energy footprint of commercially implemented adaptive cruise
control (ACC) systems and human drivers in car-following formation via
different models using empirical observations on very similar driving cycles
and/or routes. Most importantly, it initiates a critical discussion of the
findings under the behavioral properties of each mode. Findings show that: ACC
systems propagate an increasing energy consumption upstream, while human
drivers do not; they succeed in maintaining a constant time-headway policy,
operating very reliably; they develop a strong bond with their leader compared
to their human counterparts; the two modes (humans and ACCs) are operating in
different phase-space areas with room for improvement. Overall, findings show
that ACC systems must be optimized to achieve a trade-off between functional
requirements and eco-driving instructions.
