Rural two-lane two-way three-leg and four-leg stop-controlled intersections: predicting road safety effects

The study focused on grade-level rural two-lane two-way three-leg and two-lane two-way four-leg intersections with stop control located in Southern Italy, in the flat area with a vertical grade of less than 5%. The main goal is to calibrate one Safety Performance Function at two-lane two-way three-leg and two-lane two-way four-leg intersections by implementing a Generalized Estimating Equation with a binomial distribution and compare the results with yearly crash frequencies predicted by models mainly used in the scientific literature. The crash data involved seventyseven two-lane two-way intersections, of which twentyfive two-lane two-way three-leg intersections are without left-turn lane (fortyseven with left-turn lane), five two-lane two-way four-leg intersections without left-turn lane (six with left-turn lane). No right turn lane is present on the major roads. Explanatory variables used in the Safety Performance Function are the presence/absence of a left-turn lane, mean lane width including approach lane and left-turn lane width on the major road per travel direction, the number of legs, and the total Annual Average Daily Traffic entering the intersection. The reliability of the Safety Performance Function was assessed using residuals analysis. A graphic outcome of the Safety Performance Function application has been plotted in order to easily assess a yearly predicted crash frequency by varying the Annual Average Daily Traffic, the number of legs, and the presence/absence of a left-turn lane. The presence of a left-turn lane significantly reduces the yearly crash frequency values at intersections: from 0.24 to 0.031 if four-leg, and from 0.24 to 0.056 if three-leg.