You can see crossovers swooping between the outer local tracks and the center express track. Just behind me are two more crossovers; collectively, these four inter-track connections allows trains from any of the three tracks to access either side of the platform at the nearby terminal station of the Astoria Line.
Generally speaking, this is how trains get from one side of the tracks to the other when they change direction at the end of the line, and it's how two trains coming from the same direction can end up on different sides of the platform at the last station.
Day 142
Beneath the N and Q trains
May 20th, 2012
that is a great picture Matt; the shadows make it clear what is happening, maybe more than really seeing what you are talking about on the actual tracks.