  Connected and automated vehicles (CAVs) provide the most intriguing
opportunity for enabling users to better monitor transportation network
conditions and make better operating decisions to improve safety and reduce
pollution, energy consumption, and travel delays. While several studies have
shown the benefits of CAVs in reducing energy and alleviating traffic
congestion in specific traffic scenarios, e.g., crossing signal-free
intersections, merging at roadways and roundabouts, cruising in congested
traffic, passing through speed reduction zones, and lane-merging or passing
maneuvers, most of these efforts have focused on 100% CAV penetration rates
without considering human-driven vehicles (HDVs). One key question that still
remains unanswered is ``how can CAVs and HDVs be coordinated safely?'' In this
paper, we report on an optimal control framework to coordinate CAVs and HDVs at
any traffic scenario. The idea is to directly control the CAVs to force the
trailing HDVs to form platoons. Thus, we indirectly control the HDVs by
coordinating the platoon of HDVs led by CAVs.
