  This paper deals with traffic control at motorway bottlenecks assuming the
existence of an unknown, time-varying, Fundamental Diagram (FD). The FD may
change over time due to different traffic compositions, e.g., light and heavy
vehicles, as well as in the presence of connected and automated vehicles
equipped with different technologies at varying penetration rates, leading to
inconstant and uncertain driving characteristics. A novel methodology, based on
Model Reference Adaptive Control, is proposed to robustly estimate in real-time
the time-varying set-points that maximise the bottleneck throughput,
particularly useful when the traffic is regulated via a feedback-based
controller. Furthermore, we demonstrate the global asymptotic stability of the
proposed controller through a Lyapunov analysis. The effectiveness of the
proposed approach is evaluated via simulation experiments, where the estimator
is integrated into a feedback ramp-metering control strategy, employing a
second-order multi-lane macroscopic traffic flow model, modified to account for
time-varying FDs.
