Constrained ramp metering control based on sliding mode unknown input observers

In this paper, a novel ramp metering control with constraints compliance is introduced for a road traffic system with uncertain demand. The uncertain part of the flow entering the on-ramps is estimated relying on Integral Sliding Mode (ISM) based Unknown Input Observers (UIOs). The estimation is then employed in a Quadratic Programming (QP) problem, where constraints on queue lengths at the on-ramps are included via suitable Control Barrier Functions (CBFs). This results in an original approach that ensures adherence to queue length constraints by design, even under uncertain on-ramp demand conditions. The proposal is theoretically analyzed and assessed in simulation relying on the Cell Transmission Model (CTM) suitably extended to encompass the capacity drop effect. Simulation-based evaluations confirm the effectiveness of the proposed approach.