Environmental impacts and emission reduction methods of vehicles equipped with driving automation systems: An operational-level review

Driving automation systems offer both opportunities and challenges in addressing environmental issues. It is essential to clarify: (1) the environmental impacts of driving automation systems-equipped vehicles (referred to as automated vehicles, i.e., AVs in this review) and (2) the methods for leveraging AVs to improve the environment. To answer these questions, this study systematically reviews relevant literature from the past decade, focusing on the air environment and traffic operation. We also pay additional attention to the link between environmental impacts and improvement methods. The findings reveal that the environmental impact of AVs is two-sided, and it is primarily determined by connectivity, penetration rate, and traffic demand. When traffic demand is low, integrating AVs into traffic can lead to environmental improvements. However, under high traffic demand, the ability of AVs to improve the environment depends on their connectivity and the scale to form a multi-vehicle cooperation. Both micro-level traffic parameters and macro-level traffic scenarios affect the environmental benefits of AVs. While micro-parameters can be adjusted by altering the settings of AVs to realize positive environmental effects, macro-scenario conditions must be adapted by AVs through control and management methods to achieve ecological goals. Several representative methods from both vehicle control and traffic management perspectives are discussed. Generally, the existing control and management methods can be categorized into four phases: individual AV control, cooperative control of multiple AVs, facility-based management methods, and network-based ecological schemes. Finally, this study outlines five potential research directions for the sustainable development of AVs.