I have a minecart track that is 635 blocks long. There is a powered rail powered by a redstone torch every 6 blocks along the track. At each end of the track is a loop with a detector rail and redstone circuit. When a minecart crosses the detector rail, the redstone circuit powers powered rails that are angled down, thereby sending a second minecart down the track to the other end. The design intent was to always have a minecart waiting at each end of the track.

The travel time for an empty minecart to travel the entire track is approximately 2.5 minutes. I timed this by having my character run beside the empty minecart.

Scenario 1: When my character walks by a path away from the track to the other end of the track, the empty minecart is not at the end of the track as it should be. I will find it sitting part way down the track.

Scenario 2: When my character walks along the track behind the empty minecart, the empty minecart does make it to the other end of the track.

Scenario 3: When my character rides a second minecart more than 2.5 minutes after the empty minecart left, the second minecart will catch up with the empty minecart that was ahead of it. The empty minecart is still traveling along the track. I have found the empty minecart still traveling more than an hour later.

The inconsistent behavior causes the failure of the design intent to always having a minecart waiting at each end of the track. On a much shorter track, the design intent always works.