Understanding the mechanism of traffic hysteresis and traffic oscillations through the change in task difficulty level

This paper provides a detailed understanding of the mechanism of traffic hysteresis and traffic oscillations from the driver behavior perspective. Microscopic evaluation of trajectories inside seven selected oscillations is performed to obtain a comprehensive picture of these puzzling phenomena. A new method based on driver's task difficulty (TD) profile is proposed to capture changes in driver behavior in response to the disturbance caused by traffic oscillations. A close connection between the TD profile and evolution (such as formation and growth) of the stop-and-go traffic oscillations is found. Furthermore, driver behaviors inside the oscillations are identified based on driver's TD profile, and their connection with hysteresis magnitudes is established. Finally, a generalized linear model suggests that variables related to traffic flow and driver characteristics are significant predictors of hysteresis magnitude. One noteworthy finding is that, the bigger the difference between the average TD levels between deceleration and acceleration phases of a vehicle trajectory, the larger the hysteresis magnitude becomes.