Cars "sink" into nothingness mid-block if the intersections on either end of that link are unbalanced.
Say you have 200 vehicles leaving node A heading to node B, but node B is set to have only 150 vehicle arrive. That means 50 will "sink" mid block. If you have more arriving at node B than leaving node A, the reverse happens and you have a mid-block source adding new vehicles. Use the "VB" button to show you the volume-balancing on your links (the difference between entering and exiting volumes).
Mark, it only shows the unbalanced volume or balaced the link volume as well? or we need to balance manually? does it matter if the difference is less than 10% between the upstream and downstream intersections?
The vb button will only show you the difference. It's up to you to decide what, if anything, to do about it. As far as what is acceptable, I'd say that is more of a judgement and case specific decision.
If I'm looking at the two signals at a diamond interchange, I wouldn't want to show any real source/sink activity. If I'm looking at two well spaced signals with alot of drives between them, I may not even bother.
