50th Anniversary Invited Article—Autonomous Vehicles and Connected Vehicle Systems: Flow and Operations Considerations

TLDR

Autonomous and connected vehicles are expected to profoundly affect demand, mobility services, and network performance, especially in mixed traffic scenarios that will dominate during the transition to full deployment. The study examines how autonomous and connected vehicles influence traffic flow and operations in mixed traffic settings. Using elementary traffic science concepts and a microsimulation framework with varying behavioral models for autonomous, connected, and human-driven vehicles, the authors evaluate throughput and stability across different market penetration rates. Higher market shares of autonomous vehicles markedly improve throughput and stability more than equivalent shares of connected vehicles, and the framework shows that dedicated autonomous lanes are beneficial only when optional and when autonomous vehicle penetration exceeds the lane’s capacity share, while speed harmonization also yields gains.

Abstract

The impacts of autonomous vehicles, coupled with greater inter-vehicle and system connectivity, may be far-reaching on several levels. They entail changes to (1) the demand and behavior side, (2) the supply of mobility services, and (3) network and facility operational performance. We focus here on their impact on traffic flow and operations, especially in mixed traffic situations in which autonomous vehicles share the road with regular, human-driven vehicles, along with connected vehicles that may also have some automated functions. These mixed traffic situations correspond to likely deployment scenarios of the technologies, especially in the long transition towards 100% deployment. We explain using elementary traffic science concepts how autonomous vehicles and connected vehicles are expected to increase the throughput of highway facilities, as well as improve the stability of the traffic stream. A microsimulation framework featuring varying behavioral mechanisms for the three classes of vehicles is introduced. The framework is used to examine the throughput and stability questions through a series of experiments under varying market penetration rates of autonomous and/or connected vehicles; at low market shares, the impacts are relatively minor on either throughput or stability. However, as market shares increase, autonomous vehicles exert a greater influence on both dimensions compared to the same shares of connected vehicles. Applications of the framework to examine the effectiveness of selected traffic management approaches are discussed, including dedicated lanes for autonomous vehicles (good only if its use is optional and when the market share of autonomous vehicles is greater than the percentage of nominal capacity represented by that lane), and speed harmonization.