New microscopic indicators for evaluating traffic efficiency and safety

Improving both safety and efficiency in traffic systems remains a central challenge, especially in the context of increasingly mixed traffic with autonomous and human-driven vehicles. Although many indicators assess either safety or efficiency, few capture both dimensions simultaneously at a microscopic level. This paper introduces two new traffic indicators: Efficiency Index (EI), which measures local speed and spacing regularity, and Safety and Efficiency Index (SEI), which combines EI with a time-to-collision safety component. A tunable version, SEMI, allows greater sensitivity to risk by penalizing safety-critical interactions. Using real-world traffic flow data and simulation via SUMO, we tested these indicators in varying penetration rates of autonomous vehicles. The results show that while AVs improve efficiency across the board, the safety gains become especially pronounced in dense traffic. These findings offer a flexible and interpretable tool for researchers and practitioners in traffic engineering, vehicle automation, and public policy. The proposed indicators can inform the design of AV control models, traffic management strategies, and infrastructure planning where safety-efficiency trade-offs must be explicitly addressed.