ANALYSIS AND MODELING TIME HEADWAY DISTRIBUTIONS UNDER HEAVY TRAFFIC FLOW CONDITIONS IN THE URBAN HIGHWAYS: CASE OF ISFAHAN

Sayyed Mahdi Abtahi,Mohammad Tamannaei,Hosein Haghshenash

doi:10.3846/16484142.2011.635694

Sayyed Mahdi Abtahi, Mohammad Tamannaei + Show 1 more

Open Access

https://doi.org/10.3846/16484142.2011.635694

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Abstract

The time headway of vehicles is an important microscopic traffic flow parameter which affects the safety and capacity of highway facilities such as freeways and multi-lane highways. The present paper intends to provide a report on the results of a study aimed at investigating the effect of the lane position on time headway distributions within the high levels of traffic flow. The main issue of this study is to assess the driver's behavior at different highway lanes based on a headway distribution analysis. The study was conducted in the city of Isfahan, Iran. Shahid Kharrazi six-lane highway was selected for collecting the field headway data. The under-study lanes consisted of passing and middle lanes. The appropriate models of headway distributions were selected using a methodology based on Chi-Square test for each lane. Using the selected models, the headway distribution diagrams were predicted for high levels of traffic flow in both the passing and middle lanes and the relationship between statistical criteria of the models and the driver's behaviors were analyzed. The results certify that the appropriate model for the passing lane is different than the one for the middle lane. This is because of a different behavioral operation of drivers which is affected by specific conditions of each lane. Through car-following conditions in the passing lane, a large number of drivers adopt unsafe headways. This shows high risk-ability of driver population which led to considerably differences in capacities and statistical distribution models of two lanes.

Highlights

The time headway or headway is ‘the time, in seconds, between two successive vehicles as they pass a point on the roadway, measured from the same common feature of both vehicles’ (Highway Capacity Manual 2000)
In order to find an appropriate model for headway distribution, the statistical models should be used to fit the data
The process used for determining the most appropriate model for headway distribution in each lane was as follows: Step 1: for each lane, the goodness of fit models on the distribution of total headways collected from the lane was examined

Summary

Introduction

The time headway or headway is ‘the time, in seconds, between two successive vehicles as they pass a point on the roadway, measured from the same common feature of both vehicles’ (Highway Capacity Manual 2000) This parameter is one of the fundamental microscopic traffic flow characteristics. Traffic engineers and planners should be well aware of real behaviors of drivers in choosing the desired headways They should be able to predict the driver’s behaviors while facing the headways in order to have better planning and traffic managing through different conditions. This is because of the fact that time headways and their distributions would affect different flow parameters including capacity, level of service and safety (Thamizh Arasan, Koshy 2003). This may partly explain why some problems are often experienced on roadways carrying less traffic than the perceived capacity (Yi et al 2004)

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