Impact of Inclement Weather on Left-Turn Gap Acceptance Behavior of Drivers

This paper describes an empirical study conducted to quantify the impact of a number of variables on left-turn gap acceptance behavior of drivers at signalized intersections. The variables include the gap duration, the travel time needed to cross the intersection, and the corresponding weather condition. The gap acceptance data set used in the study included 11,114 observations (1,176 accepted gaps and 9,938 rejected gaps) for a permitted left-turn maneuver at a signalized intersection; the data were gathered over 6 months. The data set was divided into six weather categories for different combinations of precipitation and roadway surface conditions. Logistic regression models were calibrated to the data and compared to identify the best model for capturing gap acceptance behavior of drivers. The models reveal that drivers are more conservative during snow than rain. Drivers require larger gaps for wet surface conditions than for snowy and icy surface conditions, and drivers require the smallest gaps for dry roadway conditions. In addition, the models show that drivers require larger gaps as the distance required to traverse the offered gap increases. The study also shows how inclement weather and the number of opposing lanes affect permitted left-turn saturation flow rates. It is anticipated that these findings will be used to develop weather-specific traffic signal timings that account for changes in traffic stream saturation flow rates and also used for intelligent assistance systems for drivers.