Study on left-turn lane guidelines for signalized intersections

Left-turn lane guidelines for signalized intersections were studied by synthesis utilization of probability theory, the theory of queen and traffic flow theory. The study objective is operation efficiency. The interaction between left-turn vehicles and through vehicles and their operation characteristics were analyzed. The equation of left-turn threshold volume for left-turn lane installation at unsignalized intersections was derived. The traffic flow arrival rate was supposed as Poisson distribution. A left-turn lane guidelines modal for signalized intersections was established in view of its differences from unsignalized intersections. Two key parameters were discussed. One is the stop probability of through vehicles influenced by left-turn vehicles, and the other is the critical gap. Simulation and calculation were done for general conditions. The numerical simulations show variation laws of left-turn threshold volume for left-turn lane installation. The main influence factors of left-turn lane installation contain opposing volume, approach lane number, operation speed, cycle length and split etc. The left-turn threshold volume for left-turn lane installation drops along with the vehicle operation speed enhancement. It also decreases with the opposing volume increment, and the variation rate presents reduction tendency. It increases respectirely with the increasing cycle length, split and approach lane number, and the differences become more and more obscure with the opposing volume increment. This study presents quantitative guidelines for left-turn lane installation at signalized intersections.