The effects of changes in the traffic scene during overtaking Vassilis Papakostopoulos a, *, Dimitris Nathanael b , Evangelia Portouli b , Nicolas Marmaras b a Department of Product and Systems Design Engineering, University of the Aegean, 2 Konstantinoupoleos, GR-84100 Ermoupolis, Syros, Greece b School of Mechanical Engineering, Sector of Industrial Management and Operations Research, Ergonomics Unit, National Technical University of Athens, 9 Iroon Politechniou, GR-15773 Zografou, Athens, Greece A R T I C L E I N F O Article history: Received 3 December 2014 Received in revised form 25 February 2015 Accepted 28 February 2015 Available online 27 March 2015 Keywords: New oncoming Overtaking margins Vehicles’ interaction Video data analysis Two-lane road A B S T R A C T Overtaking maneuvers were studied in real traffic, by comparing cases where a change in the opposite traffic occurred during the overtaking maneuver i.e., appearance of an oncoming car, with cases where no change occurred during the maneuver i.e., either an already apparent oncoming car or no oncoming car. In total 45 naturally occurring cases of overtaking were analysed. By examining the time headways (TH) between the overtaking car and the other cars involved, at the end of the maneuver, a significant correlation was found between the TH to opposite traffic and the TH rear to the overtaken car. In cases where a change in the opposite traffic occurred and the proximity to opposite traffic was below a critical TH (<4 s) the appearance of a new-oncoming car caused the overtakers to actively press, both longitudinally and laterally, close to the overtaken car. In cases of overtaking where no change in the opposite traffic occurred, the TH rear to the overtaking vehicle was unaffected by the TH to the opposite traffic. Interestingly, in comparing cases where an oncoming car appeared during overtaking with cases where an oncoming car was apparent from the start of the maneuver both the TH to the opposite traffic and the duration of the maneuver were not found to be significantly different. It is suggested that drivers were probably expecting to be confronted with an oncoming car during the overtaking. However, the decreased available time to disambiguate this situation leads the overtaking driver to limit the rear safety margin of the vehicle being overtaken. The appropriateness of this practice, in terms of safety, remains questionable. ã 2015 Elsevier Ltd. All rights reserved. 1. Introduction Overtaking a lead vehicle against an oncoming one in a two- lane highway, is a highly complex task that is affected both by (i) the overtaking driver's initial judgment (i.e., prior to overtaking initiation) about whether there is sufficient time to complete a driving maneuver before colliding with an oncoming vehicle or the vehicle being overtaken (Gray and Regan, 2005; Hills, 1980), and (ii) the dynamic nature of the hazards during the overtaking (e.g., sudden appearance of a new oncoming car), leading to some modifications or even to a drastic change of the initial maneuver- ing plan (Clarke et al., 1998, 1999). The majority of overtaking studies have focused on the first issue, whereas, little emphasis has been put on whether a driver's initial judgment – even a safe one – is determinative of the way an overtaking maneuver is executed, especially at the end of the maneuver. The present study aims to shed light on this issue with a particular concern on how an overtaking driver manages the collision risk with either the oncoming vehicle or the vehicle being overtaken, under conditions of dynamic changes during the maneuver (e.g., appearance of a new oncoming car). Specifically, a class of overtaking studies on drivers' ability to estimate the required gap for passing a lead vehicle in front of an oncoming one, indicate that drivers are generally poor judges in making systematic, safe overtaking decisions (Hohm and Winner, 2010; Horrey et al., 2007; Gray and Regan, 2005; Gordon and Mast, 1970; Jones and Heimstra, 1966; Crawford, 1963). These misjudge- ments stem mainly from drivers' difficulty in estimating accurately the distance and approach speed of an oncoming vehicle under the influence of certain perceptual factors (reviewed in Tharanathan, 2012; Groeger, 2000). However, the fact that drivers' judgments are not accurate does not necessarily predetermine an unsafe or – at least – insufficient overtaking maneuver (Gray and Regan, 2005). For instance, it is * Corresponding author. Tel.: +30 22810 97133; fax: +30 22810 97009. E-mail addresses: papakostopoulos@aegean.gr (V. Papakostopoulos), dnathan@central.ntua.gr (D. Nathanael), portouli@mail.ntua.gr (E. Portouli), marmaras@central.ntua.gr (N. Marmaras). http://dx.doi.org/10.1016/j.aap.2015.02.025 0001-4575/ ã 2015 Elsevier Ltd. All rights reserved. Accident Analysis and Prevention 79 (2015) 126–132 Contents lists available at ScienceDirect Accident Analysis and Prevention journa l homepage: www.e lsevier.com/locate/aap