The south-west rule of minecarts states that minecarts will favor the south or the west direction when meeting at an intersection and the north or east direction when joining tracks. This means that when a minecart travels to a T-shaped intersection, it will travel either to the west or the south, and that when a booster resetter is made, the hooked end must face either the north or the east (unless you use the bypass I spoke of in previous posts.
Here are a few example of the south west rule in action on intersections:
|Notice how one track overlaps another? If the track on top runs east to west...|
|...your cart will travel west!|
|If track on top runs north to south...|
|...then your cart will run south!|
And here is an example of the north-east rule in action on hooked resetters:
|Only the resetters facing north and east are working at first...|
But of course, the hooked resetter can be fixed easily as described earlier.
|...but with some redstone torches, that's not a problem!|