Classification of Overtaking Situation And Manoeuvre
Overtaking manoeuvre can be defined when an action happened, where a vehicle crossed the centerline towards the opposing direction, accelerated to pass the leading vehicle and switch back to its original lane in a time so that it will not collided with the oncoming vehicle. John R McLean (1944), had classified overtaking situation and manoeuvres according to five basic descriptors:
(i) Type of overtaken vehicle
Different respond from the overtaking vehicle towards different classes of overtaken vehicles. A Jaguar may see a small, slow car as a block or delay on the road and the way the Jaguar overtake the smaller vehicle may be different from the way the Jaguar overtake a Mercedes.
(ii) Type of overtaking vehicle
The performance of the overtaking vehicle may varies according to the classes of vehicles for an example the difference performance in engine capacity to overtake between a heavy truck and saloon car.
(iii) Speed of overtaken vehicle
Speed of overtaken car may indicate how far the distance for overtaking vehicle should go in order to pass the overtaken vehicle.
(iv) Flying or Accelerative
An overtaking vehicle should analyses whether it can overtake as soon as it catches up with the overtaken vehicle ( flying) or slow down first and adjusted its speed to match the speed of overtaken vehicle before overtake ( accelerative).
(v) Form of overtaking opportunity
Overtaking opportunity can be observed through the distance of oncoming vehicle which is visible to the driver. The visibility of the oncoming vehicle may be restricted because of the sight distance.
Under the conditions of low opposing traffic, the number of flying passes (those in which the overtaking vehicle need not decelerate when approaching the impeding vehicle) will increase. As opposing flow increases, the number of passes where overtaking vehicles need to decelerate and queue behind the impeding vehicle will also increase. The increased number of these passes and the nature of the maneuver may bring about a greater number of failures. Romana (1999) observed decreasing speed differentials (the difference between the speeds of the approaching vehicle and the impeding vehicle) with increasing opposing flows. The speed differential decreases because vehicles need to queue behind the impeding vehicle before an acceptable gap appears in the opposing flow. As the queue is formed, vehicles adjust their speed to approach the speed of the impeding vehicle. Speed differential is important because as it decreases, the time the passing vehicle remains in the opposing lane during the maneuver increases. The increased exposure time leads to a higher risk of a passing failure.
In general, it would be expected that as vehicle length increases, the speed of passing vehicles will also need to increase to complete a pass within similar gaps in opposing traffic. If passing speed does not increase, the driver will either queue behind the impeding vehicle or accept an effectively smaller gap. When the driver queues for a longer time awaiting the appearance of a larger acceptable gap in the opposing traffic, congestion on the two-lane road will increase. However, if the driver does not wait for a larger gap, the passing maneuver will be made with a reduced safety margin, increasing the risk of a crash. Besides that, as the speed of the impeding vehicle increases, so does the required passing sight distance for completing or aborting the pass (Hanley and Forkenbrock, 2005)
In fact, there are number of input variables to develop the mathematical model of the overtaking behavior. The variables are impeder vehicle speed, oncoming vehicle speed, decision time of passer, headway between passer and impeder at start of manoeuvre, safety margin between passer and oncoming vehicles at completion of manoeuvre and vehicle acceleration (Roozenburg and Nicholson, 2000). While Talib Abdulameer Mahdi (1991) listed some variables for overtaking behavior study which include decision times, overtaking times, overtaking distances, safety margins, accepted and rejected gap, headways at the start of the overtaking maneuvers, headways at the finish of the overtaking maneuvers, speed of the overtaking vehicle at the end of the overtaking and acceleration of the overtaking vehicle during the overtaking.
In 1969, Farber and Silver measured decision time, accepted and rejected gaps, overtaking times and safety margins, and a time trap to measure speeds of vehicles in an overtaking behavior study. In the study, they recorded 420 overtaking maneuvers using a moving observer with an event recorder.