Although mixed traffic, including both autonomous vehicles (AV) and human-driven vehicles (HV), is expected to prevail in the foreseeable future, our current understanding of the longitudinal characteristics of mixed traffic is limited and, in particular, lacks evidence from field experiments. To bridge this gap, we designed and conducted a set of field experiments to reveal differences in car-following behaviors between a human driver following-AV and following-HV on both constant speed traffic characteristics with discrete speeds ({10,20,…,60}km/h) and dynamic car-following behaviors with continuous speeds (within 0–60 km/h) in both the indifferentiable and differentiable appearance settings of the AV. We recruited 10 drivers for the experiment (14 runs for each driver and collected position and speed data of the tested vehicles along their complete trajectories based on vehicle gaps, headways, and standard deviations of vehicle speed. A K-means clustering algorithm was applied to classify drivers based on their responses in following-AV vs. following-HV with both constant speed and dynamic speed characteristics. The analyses of the differentiable appearance setting show that different drivers exhibit different behaviors in following-AV vs. following-HV: some are AV-believers, some are AV-skeptics, and the others are insensitive. Yet in the indifferentiable appearance setting, there is no significant difference between following a lead AV and following a lead HV. This reveals that drivers’ response to the lead vehicle depends on their subjective trusts on AV technologies rather than the actual driving behavior. The results suggest that, depending on the characteristics and composition of the drivers, classic car-following behavior in pure HV traffic may need to be updated for modeling mixed traffic in the near future.

尽管在可预见的将来，混合动力（包括自动驾驶汽车（AV）和人力驱动的车辆（HV））有望盛行，但我们目前对混合动力的纵向特性的理解是有限的，尤其是缺乏现场证据实验。为了弥合这一差距，我们设计并进行了一组现场实验，以揭示人类驾驶员跟随AV和跟随HV在恒定速度交通特性和离散速度之间的跟车行为差异（{10,20，…， 60} km / h）以及在AV不可区分和可区分的外观设置中具有连续速度（0-60 km / h以内）的动态跟车行为。这表明驾驶员对领先车辆的反应取决于他们对视音频技术的主观信任，而不是实际驾驶行为。结果表明，根据驾驶员的特征和组成，在不久的将来，可能需要更新纯HV交通中的经典跟车行为，以对混合交通进行建模。