Computational Research Progress in Applied Science & Engineering CRPASE Vol. 04(02), 43-47, July 2018 ISSN 2423-4591 Estimation and Comparison of the Discharge Headway at the Outlet and Inlet Legs of Signalized Intersection Mohammad Reza Esmaeeli  , Farid Najjari Asl, Milad Hassan Zadeh Department of Civil Engineering, Iran University of Science and Technology, Tehran, Iran Keywords Abstract Signalized intersection, Startup delay, Inlet leg, Outlet leg, Average discharge headway. The time values of the saturation flow rate in signalized intersections play a key role in their schedule and performance. So far, many studies have been conducted to estimate the average discharge headway of the inlet legs of intersection, while, its values are not the same as the outlet legs due to the number of lines, driver behavior and other physical characteristics. In the present paper, with the help of the field data acquisition at five signalized intersections in Rasht city, the values of the discharge and delay time are estimated and compared in the inlet and outlet legs of the signalized intersection. The results show that the saturation conditions occur between the second and last vehicle in the outlet legs and between the fifth or sixth vehicle in inlet legs intersection. In other words, the number of vehicles with start-up delay is 1 or 2 vehicles and 4 or 5 vehicle in the outlet and inlet legs respectively. Also, the amount of saturation headway of outlet legs is less than the inlet legs. 1. Introduction The amount of several basic parameters of intersection performance, such as saturation and delay flow rates, are derivatives of the evacuation headway, so that the use of inaccurate values of discharge time point leads to incorrect estimation of the density, delay, and saturation flow rates.contributors. The evacuation headway of the vehicles is defined as the elapsed time between the vehicles on the back of each other and the stop line. The first headway, is the time interval between the start of the green phase and the time of the front wheel drive of the first vehicle from the line and the second headway, is the necessary time to pass the front wheel of the first vehicle to the front wheel of the second one of the stop line, and, to the end [1]. The headway of each vehicle decreases from its front vehicle and, with the continuation of this process, it reaches a point that from this point on, the headway will remain fairly constant until all vehicles within the queue cross the intersection or the green time is over. This constant headway is called the saturated saturated headway and can occur for vehicles from third to sixth. Of course, in different sources, there is a difference between the occurrence location of the saturation headway due to different local conditions in the data acquisition [1].  Corresponding Author: E-mail address: m.r.esmaeeli7@gmail.com– Tel, (+98) 9191506591 Received: 10 May 2018; Accepted: 30 June 2018 The sum of the difference in saturation headway with the headways of some vehicles of the first-line, which take extra time to react to the start of the green time and increase the speed, is called the initial waste time (start delay time). According to the highway capacity manual (HCM), saturation conditions occur between the headway of the fifth vehicle and the last vehicle in-line, and the time spots of the first four vehicles begin to be used to determine the delay time. Various studies have been done about delay and saturation flow rate at the intersections [2-5] and roundabout [6, 7] of Rasht, Iran. Bargegol et al. evaluated the average discharge headway at inlet legs of signalized intersections in 2015 [8]. In this regard, in the present study, by collecting the field data from 5 signalized intersections in Rasht city, the saturation evacuation headway and the start delay time in the outlet legs have been determined and evaluated with inlet legs result. 2. Literature Review The first study on the evacuation headway was conducted in 1947 by Greenshields et al. In this study, the effect of left turning was not considered. The amount of time headway for the sixth and higher vehicle was equal to 2.1 seconds and a starting delay time was equal to 3.6 seconds [9]. During the preparation of the second edition of HCM, data from 1100 signalized intersections were collected between 1955 and 1956 and the saturation headway was 2.4 seconds.