Hello there. Have you ever wondered how nice it would be to be able to switch between two track paths while cruising in your minecart? Well no need to ponder anymore, I have the perfect suggestion! Introducing the track flip sign! What this handy thing does is when placed down at a T junction of track, it forms a new T junction. But, what this does is spawns a sign (like a stop sign, but with an arrow pointing in which direction you will turn), that when struck, changes the direction you are about to go in from either the left to right, or vice versa.
Now, I still am unsure as to WHERE the sign would be, because there a variety of ways someone can build a track, or a tunnel, so I am thinking it is right on the T junction, but can be struck from farther away than normal.