  Connectivity and automation in vehicles 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. This paper investigates the
implications of optimally coordinating vehicles that are wirelessly connected
to each other in roundabouts to achieve a smooth traffic flow. We apply an
optimization framework and an analytical solution that allows optimal
coordination of vehicles for merging in such traffic scenario. The
effectiveness of the proposed approach is validated through simulation and it
is shown that fully coordinated vehicles reduce total travel time by 51% and
fuel consumption by 35%. Furthermore, we study the influence of vehicle
coordination in a mixed-traffic environment and compare the network performance
under different market penetration rates of connected and automated vehicles
(CAVs). For this particular study with near-capacity demand, due to extremely
unstable traffic, the results show that even with high penetration of CAVs
(e.g., 80%), travel time and fuel savings are much less than a network of CAVs.
