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 ( NO x ) 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. • We generalize the BA-LWR model by allowing speed-dependent acceleration bounds and derive closed-form expressions for flow and travel-time evolution at VSL locations. • We develop a discrete macroscopic link-queue representation embedding bounded-acceleration dynamics, upstream queuing, and phenomenological capacity drop at the bottleneck. • We integrate the COPERT Tier-3 emission model via trajectory-based evaluation across queue, acceleration, and cruise segments, yielding a joint travel-time and emission stage cost. • We design an emission-aware shadow-penalized one-step (SPOS) controller that internalizes bounded-acceleration-induced capacity drops while enforcing smooth speed changes and critical-density constraints. • We demonstrate via simulations that the SPOS controller substantially reduces emissions with modest travel-time impacts and is robust to stochastic demand fluctuations.