New Experimental Approach for Passing Gap Acceptance

On two-way two-lane rural highways, drivers need to pass slower vehicles to drive at their desired speed, by travelling on the opposing lane during the maneuver. Drivers take a decision before performing the maneuver, in order to accept or reject each observed gap in the oncoming traffic flow. A gap can be defined as the time or the distance between two consecutive vehicles on traffic flow. In relation to passing process, gaps can be evaluated from external points of view (static gaps measured on fixed positions) or by the driver of the passing vehicle (dynamic gaps until crossing an opposing vehicle). Both definitions are discussed and compared. However, if gaps are measured only by taking into account an opposing vehicle, it is possible to evaluate a gap with an opposing vehicle which is further than the maximum available sight distance. Then, the measured gap is longer than the observed passing opportunity. A new approach considers the effect of limited sight distance conditions, and the existence of road markings which indicates the end of passing zones. These factors have been added and a new function of probability of acceptance and rejection has been obtained, based on collected data from an instrumented vehicle in 103 maneuvers on three different road segments. Results show that longer gaps have to be replaced by their equivalent virtual gaps, which are computed until crossing an opposing vehicle which could appear at the end of the visible area, before the real vehicle comes.