A bounded acceleration framework for emission-aware variable speed limit control

Urban traffic congestion significantly impacts regional air quality and contributes substantially to pollutant emissions. Suburban freeway corridors are a major source of traffic-related emissions, particularly carbon monoxide (CO), nitrogen oxides (NOx) and hydrocarbons (HC). This paper proposes an emission-aware receding-horizon Variable Speed Limit (VSL) controller with a shadow-penalized one-step update rule for peripheral freeway corridors. Emission rates on freeways exhibit high sensitivity to speed fluctuations and congestion recovery processes. To address this relationship, we generalize the bounded-acceleration LWR (BA-LWR) traffic flow model by allowing the acceleration bound to depend on speed and deriving analytical expressions for flow and travel times. This BA-LWR variant enhances behavioral realism through the incorporation of driver responses to congestion, which is widely recognized as a main cause of the important capacity drop phenomenon. Our approach implements dynamical optimization of a VSL to balance the dual objectives of minimizing both travel time and emissions as quantified by the COPERT V (European Environment Agency, 2023) model. Numerical simulations demonstrate that this framework effectively manages congestion and reduces emissions across various traffic demand scenarios.