Impact of Fog Conditions on Lane-Level Speeds on Freeways

Abstract

Few studies have focused on the impacts of fog conditions on lane-based speeds on freeways. To explore speed differences and to predict speeds under fog conditions, this paper analyzed the historical traffic data and meteorological data at two freeway sections in Shanghai, China. The Kolmogorov–Smirnov test was used to compare speed distributions between the different levels of visibility. Multiple linear regression models for two sections with different numbers of lanes were established to predict speeds, in which lane number was used as an explanatory variable. It was found that the impacts of reduced visibility on speed distributions and speeds vary with visibility level, lane number, type of vehicle, day of the week, time of day, and the number of lanes. More importantly, the impacts of reduced visibility on mean speeds and speed distributions are different at sites with different numbers of lanes. The results can assist traffic management agencies to better implement variable speed limits for the fine management of lane levels under fog conditions.