Jurnal Kejuruteraan 32(2) 2020: 187-195 https://doi.org/10.17576/jkukm-2020-32(2)-02 A Study on Following Behavior Based on the Time Headway Ehsan Ramezani Khansari, Masoud Tabibi* & Fereidoon Moghadas Nejad Civil Engineering Department, Amirkabir University of Technology, Tehran, Iran Corresponding author: masoud.tabibi@chmail.ir Received 22 March 2020, Received in revised form 5 April 2020 Accepted 21 April 2020, Available online 30 May 2020 ABSTRACT While time headway (TH) is a relatively simple variable and has been well researched, it has been less explored in non-lane-based traffic. The main aim of this paper is considering lateral distance in studying TH in a non-lane- based traffic flow. In this study driving behavior, speed-TH relationship, and the following threshold by using only TH in a non-lane-based flow were investigated. In a novel approach, THs were segmented into five intervals in a step by step manner from smallest to largest THs. Considering lateral distance led to divide driving behavior into intervals (based on the average TH), including: Unsafe (0-0.7 sec), non-lane-based car-following (0.9 sec), lane- based car-following (1.0 sec), overtaking TH (1.3 sec), and free driving (larger than 2.5 sec). It was founded that the TH of starting overtaking maneuver can be a good criterion to distinguish between following and free driving behavior. Also, in lane-based car-following behavior, when lateral distance between the following and preceding vehicles was not considerable, the smallest THs were seen. It has happened around the average speed of the flow as the driver may adopt lower THs because of the tendency to overtaking. Linear relationship was found between TH and lateral distance in non-lane-based car-following conditions. TH of non-lane-based behavior is less than lane-based and smaller THs would force drivers to apply lateral distance or vice versa. Keywords: Time headway, Driving behavior, Non-lane-based behavior, Free driving INTRODUCTION The time headway (TH) or headway of vehicles is important in terms of safety and traffic flow characteristics, as one of the main goals of car- following models is estimating headway, implicitly or explicitly(Helbing and Tilch 1998; Lenz, Wagner, and Sollacher 1999; Aghabayk et al. 2014). For instance, Pipes and Forbes provided equations for speed-headway and speed-TH, respectively, to directly estimate the headway in a steady-state flow (Cao and Yang 2009; Brackstone and McDonald 1999). Although TH has been studied in many researches since 1936 (ADAMS 1936), it is still the main topic of many papers, for example, in 2002, Newell tried to developed Pipes model by considering the non-linearity (Newell 2002; Ahn, Cassidy, and Laval 2004) and, in 2017, Khansari et al. studied the distribution of TH in different lanes (Khansari, Tabibi, and Moghadas Nejad 2017). Furthermore, the study of headway can help us for a better understanding of the drivers' behavior. There are, of course, a few studies in this regard. Although some researchers, such as Fritzsche and Wiedemann, divided the driving behavior based on multiple variables (Olstam and Tapani 2004), they needed a lot of variables and complex calculations. In other words, these models cannot easily be used in other situations and require some complicated calculations (Aghabayk Eagley 2013). The following threshold has been the main topic of many papers and it may be estimated by studying TH. The following threshold is defined as the headway span, in which the driver would be affected by her/his leader car (Vogel 2003). In other words, the rear vehicle would enter the following condition by decreasing the headway to a threshold. The following threshold should be determined in the car-following models, which it is usually assumed solely based on the conditions of the recorded data without plausible logic. For example, Amini et al. compared personal car-motorcycle with motorcycle car-following behavior by mounting a camera at the height of 40 m. They selected 100 m as following threshold, only because of the recordable length of the road(Amini et al. 2018). Some researchers examined the following threshold. Al-Jameel suggested 80 m as the optimum following thresholds by building and examining different GHR (Gazis-Herman-Rothery) car- following models (Al-Jameel 2009). Aycin investigated different thresholds in deceleration situation. It was observed that the follower vehicle was not affected by lead vehicle when the spacing between the following and its leading vehicle is greater than 76 m (Aycin 2001). Herman studied the oscillation between the acceleration and deceleration situations and determined 61 m as following threshold (Chandler, Herman, and Montroll 1958). Some of the researchers have tried to estimate the following threshold based on TH. Evans and Wasielewski (1983) proposed 2.5 sec TH as the upper limit for interacting vehicles, based on a brought to you by CORE View metadata, citation and similar papers at core.ac.uk provided by UKM Journal Article Repository