Multivariate Analysis of Freeways Speed and Time Headway Under Mixed Traffic Streams

Abstract

Speed and time headway are the fundamental microscopic traffic flow characteristics that are useful in developing microscopic traffic simulation models, driver behavior analysis, safety evaluation, capacity estimation, and level of service analysis of a freeway segment. Many studies have focused on speed and time headway analysis under lane-disciplined and homogeneous traffic conditions, whereas limited studies have been conducted under weak lane-disciplined and mixed traffic conditions. Also, speed and time headway distributions are often not analyzed together. Vehicle speeds and arrival times are considered independent traffic parameters in the traffic simulation process, ignoring the correlation between vehicle speed and headway. The present paper intends to provide a report on the results of a study aimed at investigating and analyzing the effect of the different traffic flow and density levels on speed and time headway distributions of freeways under mixed traffic conditions. A large amount of speed and time headway data was collected using the Transportable Infra-Red Traffic Logger (TIRTL) instrument from three different intercity highways in the state of Tamil Nadu, India. Distribution of speed and time headway has been studied for various traffic flow and density levels. The Kolmogorov-Smirnov (K-S) test is used as the goodness-of-fit test to assess the statistical validity of each probability distributions before choosing the best fit distribution. The results from the study indicate significant variation in speed and time headway distributions and finally shows that the speed and time headway follow different probability distribution patterns under different traffic flow and density levels.