Integrated macro-micro control framework for highway active safety

Abstract

This paper presents an integrated macro-micro control framework for enhancing active safety on highways, where crashes frequently arise from speed differentials in congested flow. The framework couples a macroscopic layer, comprising a density-based variable speed limit (VSL) controller and an ALINEA ramp metering (RM) controller that regulate aggregate flow, with a microscopic layer that issues in-vehicle alerts when the time-to-collision (TTC) between consecutive vehicles falls below a congestion-dependent threshold. The two layers are linked through the bottleneck segment speed, which both drives the macro control actions and shapes the micro-level car-following conditions. A hybrid simulation model combining the METANET macroscopic traffic flow model with the Intelligent Driver Model (IDM) is developed to evaluate the framework across three congestion scenarios. Results show that the integrated VSL plus RM strategy reduces total travel time by up to 12.2 percent under heavy congestion, while the adaptive TTC-based alert system provides complementary safety gains by issuing proactive warnings in free-flow conditions and reducing alert fatigue in congested conditions. The framework demonstrates that coupling network-level management with vehicle-level safety intervention yields efficiency and safety benefits that neither layer achieves alone.