The passing maneuver (PM) on two-lane rural highways is a very complicated driving task because it is associated with the risk of a head-on collision. It can be more risky for multiple PMs where a single vehicle passes at least two other ones. Using the time-to-collision (TTC) indicator, this paper addressed the risk of multiple PMs and developed a logistic regression model to predict the occurrence probability of a serious head-on conflict defined with a TTC of <3 sec-threshold. The effective accepted gap (EAG), passing duration, number of passed vehicles, and the end position of maneuvers were the explanatory variables and the data used to estimate the model were collected from 319 PMs using a drone at seven passing zones in Iran. Results indicated that 85% of the passing vehicles were safe in a single PM with EAGs greater than 22.4 sec for all types of passed vehicles. This safe EAG increased by up to 30.9 sec for vehicles involved in multiple PMs with two passed vehicles and 52 sec for those with three or more. Heavy vehicles required 3.1 sec more EAG than passenger cars to conduct a single PM and maneuvers ended in no-passing zones were more risky than those ending in a passing zone.
Keywords: Accepted gap; Multiple passing maneuver; Passing zone; Risk; Safety measure; Time-to-collision.
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