Analysis Of Capacity At Unsignallized T-intersections Based On Gap Acceptance Heory

Analysis of capacity at unsignalized T-intersections based on gap acceptance theory includes four parts:the characteristics of the major road’s time headway and speed,the estimation of critical gaps’ distribution,the derivation of unsignalized T-intersections minor traffic capacity model and the comparison between the VISSIM result and model estimation.Time headway and speed of the major road are the important factors of studying unsignalized T-intersections traffic capacity.The paper collected data of three typical unsignalized T-intersections’ speed and time headway in Tongliang District,Chongqing.Analyze the effects of minor road’s angle to the vehicle speed and discrete of vehicle speed in the major road.It concluded that try to avoid using minor road’s angle was not 90° and transition zone unsignalized T-intersections to shunt the major road’s traffic flow.Provide advice to improve the capacity of road network and unsignalized T-intersection.For unsignalized T-type intersection,finding out the reasonable estimation distribution of critical gaps has important significance to the study of capacity.By considering the effect of time headway distribution on major stream,analyzing the condition of safe distance,passing time and the relationships among space headway,time headway and speed by using the principle of the kinematics on the basis of vehicle safety distance model,construct the expression formula of critical gaps.Prove critical gaps obeying the Poisson distribution of considering the driver’s reaction time.The model of the minor traffic capacity is based on the estimation of time headway of the major road and critical gaps’ distribution.On the gap acceptance theory,using critical gap of Poisson distribution of considering the driver’s reaction time,analyzing four cases of major headway of Shifted-exponential or M3 distribution,driver behavior of homogeneous and inconsistent or nonhomogeneous and inconsistent to set up unsignalized T-intersections minor traffic capacity model.Simulate the actual reaction times to calibrate model’s parameters.Use the impedance factor to calculate the whole unsignalized T-intersection’s capacity.Compared the common methods result,theoretical methods result with the actual maximum capacity,find out the theoretical result is more accord with the actual maximum capacity.Simulate the capacity of three unsignalized T-intersections by using VISSIM.Compared the simulation result with the common methods,theoretical methods and actual maximum capacity,find out the simulation result is greater than the actual maximum capacity.The actual maximum capacity is influenced by the driver’s reaction time.The driver’s reaction time is influenced by the geometrical characteristics and main road traffic of the intersection.The simulation result didn’t consider the driver’s reaction time.