Urban Road Traffic Fuel Consumption Optimization via Variable Speed Limits or Signalized Access Control: A Comparative Study

Othman, Bassel; De Nunzio, Giovanni; Di Domenico, Domenico; Canudas-de-Wit, Carlos · 2021 · Crossref

DOI: 10.1109/cdc45484.2021.9683194

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Summary

This study compares the ecological potential of two traffic control strategies—Variable Speed Limits (VSLs) and signalized access control—to optimize fuel consumption and reduce pollutant emissions in urban road networks. The research is motivated by the need to improve air quality and energy efficiency in cities, where traffic-related pollutants remain above recommended limits. While VSLs are known to impact traffic dynamics, previous studies often overlooked the performance implications for peri-urban areas. This paper addresses this gap by evaluating how these control actuators affect both urban and peri-urban regions simultaneously. The authors developed a synthetic two-region network consisting of an urban area and a peri-urban area. Traffic dynamics were modeled using an adapted macroscopic Cell Transmission Model (CTM) within a Nonlinear Model Predictive Control (NMPC) framework. To predict fuel consumption, the CTM was coupled with an Artificial Neural Network (ANN) trained on 3.5 million data points from microscopic simulations of Euro 4 diesel vehicles. The ANN inputs included current and previous densities, speeds, speed limits, and traffic light states. The control strategies were evaluated using the microscopic traffic simulator SUMO, calibrated with real-world driving data from French cities. Physical models based on Newton’s laws of motion were used to calculate wheel force, engine torque, and subsequent fuel consumption and NOx emissions. Three scenarios were simulated over one hour: an uncontrolled baseline, a VSL-controlled scenario, and a signalized access-controlled scenario. The VSL controller dynamically adjusted speed limits in the urban area between 20 km/h and 50 km/h, while the access controller regulated the duty cycle of traffic lights at the interface between the peri-urban and urban areas. Results showed that VSLs significantly improved energy efficiency in both the urban area (18% reduction in fuel consumption) and the peri-urban area (14% reduction). Similarly, NOx emissions decreased by 18% and 13% in the respective areas. In contrast, signalized access control only improved metrics in the urban area (7% fuel reduction, 6% NOx reduction) while causing a deterioration in the peri-urban area (21% increase in fuel consumption, 19% increase in NOx). The study concludes that VSLs are more promising for holistic network optimization because they induce smoother density variations, whereas signalized access control forces vehicles in the peri-urban area to stop and start, which is highly energy-intensive. VSLs also improved total travel distance in both areas, while access control slightly worsened urban travel distance. The findings suggest that VSLs offer a superior compromise for balancing environmental sustainability and traffic performance across interconnected urban and peri-urban zones.

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• speed management