Analytical Study of Headway Time Distribution on Congested Arterial: A Case Study Palestine Road in Baghdad City

Abstract

The time headway is important parameter in traffic flow theory and broadly applied in different branches in transportation engineering. In this research the one of the major arterial street in Baghdad city is Palestine arterial street that have been selected as a case study to investigate the distribution of time headway under heavy flow conditions. Collected field data for tow links; Link (1) from Al-Mawal intersection to Bab AlMutham intersection 1.03 km length and link (2) from Zayona intersection to Mayslone intersection is obtained at two different time periods to conform the variation of time headway under congestion periods. The variation in time headway for Link (1) is reduced and more constant state is obtained due heavy flow conditions at congestion peak periods. The situation is not the same on Link (2), the fluctuation in time headway is still observed at higher flow rate. This demonstrated the effect of land use characteristics on time headway distribution and vehicle arrivals. Both Shape for the distribution of probability density function is skewed to the right and the peak rises for link (1) and its higher than for link (2). This illustrated that the peak value for probability density function is higher on link (1) which implies high flow rate at congestion periods. The Logostic probability distribution function is used to probably describe the time headway at congested Palestine arterial street for link (1) and (2). The fitted field data of time headway for different range of scale parameter from 1.5 to 0.85 are obtained. Goodness of fit using Chi Square non- parametric test is applied in this research to explore how the theoretical Logostic distribution fits the empirical data for time headway distribution.