Effects of variable speed limits on traffic operation characteristics and environmental impacts under car-following scenarios: Simulations in the framework of Kerner's three-phase traffic theory

Variable speed limits (VSL) strategies have been demonstrated to successfully improve traffic dynamics characteristics. However, the effects of the strategies on overall traffic performance from the perspective of Kerner's three-phase theory has yet to be needed. This paper attempts to present a comprehensive simulation study on this topic. The study investigates the effects of VSL strategies on traffic operation characteristics and environmental impacts by combining the Kerner-Klenov car-following model and a practical VSL control algorithm. Simulations have been carried out for different control scenarios. The simulation results quantitatively indicate how and to what extent the VSL strategies affect overall traffic performance, including fundamental diagram, local speed variance, VSP distributions and average exhaust emission rates. It is revealed that the implemented VSL strategies cannot either improve maximum flow rate or prevent from the occurrence of the F→S transition. However, VSL lead to a significant extension of occupancy range for synchronized flow phase and suppress speed variability in traffic stream in congested traffic state, especially in the jam phase and the transitional state S→J. Moreover, the VSL strategies is able to reduce traffic emissions by improving VSP distributions and average emission rates in the synchronized and jam phases. These findings suggest that the perspective of Kerner's three-phase theory can be added to the development of VSL control algorithms which aim to achieve high traffic efficiency with minimum traffic environmental impacts.