Abstract:Traffic oscillations, an unpleasant form of traffic congestion, have attracted the attention of researchers for years. When viewed in the so-called flow–density or speed–density phase plane, oscillatory traffic states often present themselves in the form of hysteresis loops. In this paper, the impacts of driver relaxation and anticipation on traffic flow are examined, and their link to traffic hysteresis is sought. Through an analysis of the trajectory data from NGSIM and a theoretical analysis of car-following models, it is revealed that traffic hysteresis is generated by an imbalance in driver relaxation and anticipation. Changing the strength of relaxation and anticipation can reproduce positive, negative, and double hysteresis loops, as well as aggressive and timid driving behavior. It is further shown that the relative positions of acceleration and deceleration phases with respect to the equilibrium state are not unique and are determined by the comparative strength of relaxation and anticipation in different traffic conditions. This study suggests that traffic hysteresis can be suppressed by balancing driver relaxation and anticipation, and stop-and-go traffic can be smoothed by eliminating aggressive driving in congested traffic.