Capacity and delay are two most important measures in the evaluation of non signalized intersection’s performance that have been widely used in traffic improvement projects and transportation network assignment models. Because of the close relation between driver behaviors and traffic regulations with the Investigation and computation of delay and capacity in non signalized intersections the analysis of these intersections are so sophisticated. The purpose of this research is to adapt the state of the art algorithm used in HCM 2000 with Iran’s situation with respect to the gap acceptance behavior of the drivers in Iran. The data achieved from several field observations on the intersections of Tehran have been used to calibrate the gap acceptance used for the capacity and delay estimation model. Using developed countries design and operation manuals in developing countries without modification would give misleading results.

When the degree of saturation at intersection approaches one, Webster’s optimum cycle length equation becomes inapplicable, because the cycle length will becomes very big when the degree of saturation approaches one and will be fully unrealistic when the degree of saturation becomes greater than one. This is not a problem for HCM2000 method. But optimum cycle length calculation in this method has not specific equation and based on try and error to minimize delay time. Also this method requires many input parameters that made it expensive. In this paper new modified Webster’s optimum cycle length equations for some specific situation of geometric and phasing based on HCM2000 method have been presented that have not described problem. The purpose of this paper is ability to use of “total lost time within the cycle (L)” and “the sum of critical phase flow ratios (Y)” parameters and creation new minimum cycle length equation based on HCM2000 method. Regarding to this fact that intersection geometry and phasing is related to the optimum cycle length, four situations of intersection have been considered. After this stage the following step by step procedure was used: - having low traffic volume and low “L” - using “HICAP2000” software to calculate optimum cycle length-also using Webster’s equation to calculate optimum cycle length-increasing traffic volume and repeating the above steps-the above steps continue until degree of saturation at intersection approaches one-increasing “L” and repeating above steps - with renewed increased “L” and repeating above steps we have optimum cycle length for many of “L” and traffic volume at specific intersection After this method we used “SPSS” software to modeling new relationship between “L” and “Y” and finally new equations are presented for four situations of intersection. This method can be expanded for other geometry and phasing intersections. 

2Two-lane intermunicipal highways serve two functions in the highway network: mobility and accessibility. To estimate the level of service on two-lane, two-way highways two performance measures are used: Percent Time Spent Following (PTSF) and Average Travel Speed (ATS). Due to the difficulty of measuring PTSF in the field, Highway Capacity Manual (HCM2000) suggests a surrogate measure to estimate the PTSF in the field, that is, the percentage of vehicles traveling with headways of less than three seconds. The present research tries to evaluate validity of this surrogate measure in Iran. For this purpose, traffic flow was analyzed in three intermunicipal two-lane highways with inclusive counter. By using the counter data in these roads, the percentage of vehicles with headways of less than three seconds in various intervals is measured, and then using IHSDM software, traffic flow and geometric qualifications of routes in each road are simulated. The results show that values of PTSF from simulating is very close to surrogate measure, namely percentage of vehicles with headways of less than three seconds. Paying attention to traffic and geometric qualifications in Iran's roads, this research shows that surrogate measure may be used for measuring PTSF.

Roundabout is one of the most effective intersection control methods in the world. Although, they have often been used in Iran, but, the methods which are proposed to analyze roundabouts are very old and new regulations are not implemented for analyzing modern roundabouts. There are strong needs to apply new modern analyzing methods for studying roundabouts in Iran. Also, these methods should be compared with other methods for controlling intersections. The results from previous studies show that roundabouts perform better than the intersection with two-way stop and all-way stop control in various cases. The most important aim of this research is to compare the capacity and delay of roundabout with signalized intersection at the same conditions. In this paper, the methods which are applied in the developed countries for calculating the capacity and delay of roundabout are considered and the most effective and suitable one is chosen for using in Iran. The method of Australia was selected and proposed for analyzing roundabouts. For analyzing the capacity and the delay of signalized intersection the HiCAP software was used. This software works based on HCM2000 theoretical model. Two signalized intersection of Isfahan city were selected for the case study. The roundabout plan was used in the same situations with the same space and traffic data. The diagram of entrance delay and capacity of roundabout and signalized intersection was obtained and analyzed. One of the main results of this analysis is that a two-lane roundabout in same space intersection with inscribed circle diameter of 55 to 60 meter can pass about 3400 vehicles per hour with lower delay comparing to intersection. Another result is preference of roundabouts in low and medium volumes comparing to intersections. In such volumes roundabouts have very low delays comparing to intersections. As an important point, this research shows capability of the selected method for analyzing roundabout and represents formula calibration with regard to Iran conditions.

The aim of the present study is to analyze the capacity of the basic Multi-Lane Highway Segments and to investigate the relationship between the capacity and the behavioral characteristics of Iranian driver population. The case study was Shahid Kharrazi multi-lane highway in Isfahan. Under uninterrupted flow conditions, the capacity of different lanes was calculated using both macroscopic and microscopic approach. For the first approach, three macroscopic speed- density models were used including the Greenshields linear model, Greenberg logarithmic model and Underwood exponential model. For this purpose, the main traffic parameters such as flow rate, mean speed and density were obtained for different day-time and night-time periods. In order to implement the capacity analysis through the microscopic approach, the vehicle time headway data were extracted. The results related to the both approaches indicate that the capacity values of Iranian multi-lane highways lead to higher amounts than the value proposed by Highway Capacity Manual (HCM2000). It seems that the most important reason is the distinct behavioral characteristics of Iranian driver population, rather than HCM study-population. The inclination of a large part of Iranian drivers to choose unsafe headways and non-compliance with safe distance through car-following process has caused increased capacity. Nevertheless it has increased the risk of accident and has caused reduction in the driving safety. Other results of this paper indicate that the driver's behavior patterns in different lanes are heterogeneous. This has led to the fact that traffic parameters such as capacity have had considerable discrepancy for different lanes. It is also inferable that the capacity decreases at night-time hours about 2 till 8 % due to more cautious behavior of drivers.