# Effects of Anthropomorphic Driving Vehicles on Traffic Flow
## 1 Introduction  
Over the past four decades, the rapid development of autonomous driving has not only increased driving comfort and safety, reduced emissions, and increased convenience for people with disabilities, but has also brought about new hope for optimizing traffic flow and reduce traffic congestion [1, 2, 3, 4]. In the realm of autonomous driving, many achievements are centered around autonomous driving decision making and control, involving machine learning, deep learning, and artificial intelligence (AI) [5, 6, 7]. At the same time, the implementation and application of connected autonomous vehicles (CAVs) is also a research direction that has received much attention in the field of autonomous vehicles [8, 9, 10]. The improvement in mobility is an unintended effect of autonomous vehicles. Vehicles with different levels of automation, including driving-assisted vehicles, partially automated vehicles, and fully autonomous (self-driving) vehicles, all alleviate traffic congestion to different degrees [11, 12, 13]. Unlike connected vehicles, which alleviate traffic congestion mainly by reducing or avoiding stop-and-go traffic through vehicle-to-vehicle communication [14, 15], the positive effect of autonomous vehicles on traffic is mainly due to theshortened reaction time and expected distance from the vehicle in front (desired headway) [16; 17]. In comparison, the barriers to the implementation of CAVs are greater than those for autonomous vehicles. In addition to price and technical issues, CAVs also present more issues such as vehicle privacy and public acceptance [18; 19; 20]. Autonomous vehicles have many advantages, but their implementation also faces many challenges. In the early stages of the implementation of autonomous cars, public acceptance has an important impact on their popularity. Comfort and trust are important indicators that affect public acceptance. The machine-like behaviors of autonomous driving cause many problems that can be solved by anthropomorphic driving. In terms of driving comfort, autonomous vehicles make users lose control and unable to predict future trajectories, causing motion sickness (autonomous carsickness) [21]. In addition, all motion sickness issues represent a concern across all automation levels [22]. Anthropomorphic driving makes human-like driving characteristics possible in terms of trajectory planning [23], lane changing [24], speed maintenance [25], etc. These decision-making tools can be used to mitigate the effects of these driving modes on physiological well-being [26; 27]. In terms of user trust and acceptance of autonomous vehicles, many studies show that human-like driving styles also increase user trust in autonomous driving [27; 28]. Whether a driver chooses autonomous driving usually depends on their assessment of comfort, safety, and trust [27]. Anthropomorphic driving absorbs the characteristics of human driving to increase comfort and trust without replicating human mistakes. Human driver-related errors have always been a significant contributor to vehicle-related traffic accidents [29; 30; 31], accounting for as much as 80-94% of traffic accidents [29]. The risk factors of human drivers that cause accidents, such as alcohol, fatigue, and driver distraction, are all completely avoidable by a machine that does not become drunk, fatigued, or distracted. In addition, other reasons for human driver accidents, including unfamiliarity with a road [32] and poor prediction of other vehicles' behaviors [33; 34], are alleviated by anthropomorphic autonomous driving, with machines completing road observation. Both low-automation driver assistance vehicles and high-automation self-driving cars have been proven to be beneficial in alleviating traffic congestion and increasing traffic capacity [11; 12; 13]. The use of anthropomorphic autonomous driving vehicles may become inevitable for the implementation of autonomous driving vehicles. Will anthropomorphic autonomous driving vehicles reduce the positive impact of autonomous driving cars on traffic?