Capacity Analysis of the Basic Multi-lane Highway Segments (A case study for Shahid Kharrazi multi-lane highway in Isfahan)

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.