About BackTrack Occuring near the Pick-Up Event

The following factors are taken into consideration when Schedule Server checks for backtracking near pick-up events:

  • Distance Threshold (DT) - The distance in meters between a client pick-up location and an intermediate event, which, when exceeded, triggers backtrack checking. It is also used as the Origin Retrenchment Threshold (ORT) by defining the radius of the circle around the origin within which travel can occur without incurring a BT violation.
  • Origin Retrenchment Ratio (ORR) - A value expressed as a percentage of the DT that is intended to draw the boundary for re-entering the pick-up area (origin) with respect to the furthest point driven from the point of origin.

To define the boundaries for backtracking from an origin event, the distance is measured from the pick-up location to the first event that takes place outside of the Distance Threshold to determine the origin reference distance (ORD). The length of the ORD is multiplied by the user-defined Origin Retrenchment Ratio (ORR) to determine the radius of the circle around the origin pick-up event, which indicates whether a vehicle is considered to be backtracking. Any pick-up or drop-off events within this circle generates a Backtracking violation (BT) for the corresponding drop-off event.

For example, the following diagram illustrates how Schedule Server checks for backtracking near a pick-up event:
Schedule Server checks for backtracking near a pick-up event

Assume that the DT, represented by the orange circle, is set to 600m, and the ORR is set to 30(%) in the Origin Retrenchment Ratio. The distance from Pick-Up 1 (PU1) to Pick-Up 2 (PU2) is 1000 meters, which determines the radius of the ORD, represented by the black circle, because PU2 is the first event that takes place outside of the distance threshold. Multiply the ORD by the ORR (1000m x 30% = 300m) to get the radius of the Origin Backtracking Circle (OBC), represented by the red circle, in which backtracking is flagged.

In this example, events such as Pick-Up 3 (PU3) generate a BT violation, which is indicated in the run itinerary beside Drop-Off 3 (DO3) (see When Backtracking Occurs Near the Drop-Off), the corresponding drop-off event, because they occur within the OBC. However, events such as Pick-Up 4 (PU4) does not generate a BT violation because they occur outside the OBC.