>>1295798gotchu pham
check out the track map on the right of pic related. For reference, the bridge at the back in the photo earlier is on the left of the map.
So, here you see the two alignments, on top and on the bottom. Lines 3 and 15 use the bottom alignment, lines 6, 7 and 10 use the top alignment, plus line 4 uses the "bypass alignment" on the left.
Line 3 runs from the bottom right to the left (onto the bridge) and vice-versa, line 15 runs from the top right to the bottom left.
Lines 6, 7 and 10 all run from the top right to the left.
Line 4 runs from the bottom left to the left.
It sounds confusing, but the point is to spread out a total of five lines (not counting line 4) onto the two alignments, and to avoid lines unnecessarily crossing each other. The bottom alignment is used by the lines that run to and from one of the bottom directions, the top alignment is used by the lines using only the top directions.
All clear now, yes?