Variable speed limit modelling to improve traffic safety and efficiency of mixed traffic flow by a two-stage framework

AbstractA two-stage variable speed limits (VSL) modelling framework is proposed to enhance traffic safety and efficiency at freeway bottlenecks with mixed traffic flow comprising both human-driven and autonomous vehicles. The first-stage macroscopic VSL control framework is based on an extended cell transmission model (ECTM) and a VSL optimal control model. The ECTM serves as a traffic state predictor and characterises mixed traffic flow by modelling various characteristics such as driving behaviours and flow performance. The ECTM-based optimal control model aims to improve safety and efficiency. The second-stage microscopic validation framework is designed using the VISSIM_COM to validate the effectiveness and sophistication of the proposed VSL strategy. The proposed strategy is compared with a fixed speed limit strategy (FSL) and a VSL strategy considering only efficiency improvement (VSL_E). The results demonstrate that the proposed strategy improves traffic efficiency compared to the FSL and significantly outperforms VSL_E in traffic safety.KEYWORDS: Variable speed limit modellingsimulation validationmixed traffic flowextended cell transmission modeltraffic safety and efficiencyfreeway bottleneck Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThis work was supported by National Natural Science Foundation of China [grant number 71901223]; Natural Science Foundation of Hunan Province [grant number 2021JJ40746].