The A-track cut-thru is a joining section of track that creates the shorter A-track.  This turn becomes Turn 4 of the A-track and leads to Turn 14 of the C-track.  This corner is directly opposite turn 4 of the C-track.  This is quite a difficult corner on the A-track as it makes the transitions from left to right through the turns quite quick and difficult to judge.

This section of track is commonly used on the roll-up laps of the C-track to save time with smaller fields driving the entire circuit to form up.