Impacts of Autonomous Vehicles on Traffic Flow Characteristics under Mixed Traffic Environment: Future Perspectives

Abstract

Vehicle automation and communication technologies are considered promising approaches to improve operational driving behavior. The expected gradual implementation of autonomous vehicles (AVs) shortly will cause unique impacts on the traffic flow characteristics. This paper focuses on reviewing the expected impacts under a mixed traffic environment of AVs and regular vehicles (RVs) considering different AV characteristics. The paper includes a policy implication discussion for possible actual future practice and research interests. The AV implementation has positive impacts on the traffic flow, such as improved traffic capacity and stability. However, the impact depends on the factors including penetration rate of the AVs, characteristics, and operational settings of the AVs, traffic volume level, and human driving behavior. The critical penetration rate, which has a high potential to improve traffic characteristics, was higher than 40%. AV’s intelligent control of operational driving is a function of its operational settings, mainly car-following modeling. Different adjustments of these settings may improve some traffic flow parameters and may deteriorate others. The position and distribution of AVs and the type of their leading or following vehicles may play a role in maximizing their impacts.

Modeling the Car-Following Behavior with Consideration of Driver, Vehicle, and Environment Factors: A Historical Review

“…Ahmed et al [15] reviewed the car-following behavior models used to describe manual and autonomous vehicles in simulation software. In the same period, Al-Turki et al [16] reviewed the research on traffic flow characteristics under different penetration percentages of AVs based on car-following behavior. Biswas et al [17] reviewed the research on headway, a key indicator to describe car-following behavior.…”

“…These reviews contribute substantially to the research. Among the reviews, [7] involved the driver factor, and [9,10,[14][15][16] involved the vehicle factor. To be specific, [9,[14][15][16] reviewed the research involving intelligent and connected technology.…”

“…Among the reviews, [7] involved the driver factor, and [9,10,[14][15][16] involved the vehicle factor. To be specific, [9,[14][15][16] reviewed the research involving intelligent and connected technology. However, these works are limited to AVs along with their impacts on traffic flow.…”

Environmental Impacts of Connected and Automated Vehicles Considering Traffic Flow and Road Characteristics

“…GHG emissions from the transport sector have steadily increased with a net growth of 21% between 1990 and 2018 (1). In a conventional driver-operated vehicles (DOVs) traffic environment, traffic flow efficiency and capacity are dependent on the human driving behaviour, which is stochastic in nature (2). Driving behaviour includes response times, desired speeds, headway distances, lane change performance, acceleration and deceleration rates and different reactions to traffic shockwaves and disturbances.…”

“…Driving behaviour includes response times, desired speeds, headway distances, lane change performance, acceleration and deceleration rates and different reactions to traffic shockwaves and disturbances. Connected and automated vehicle (CAV) technologies provide the capability of vehicle-to-vehicle communication and vehicle-to-infrastructure communication, allowing CAVs to adjust their driving behaviour in real-time (2). In addition, CAVs have the potential to increase road capacity and cost savings by reducing congestion and crash risks (3).…”