BeltSwitch brings control over transport belts to YOU! Hover over them and toggle alt mode, to change them into their new circuit CONTROLLED mode! Just give them a 'T' signal, and watch them turn!

The signal is taken mod 4 for north/east/south/west 0-3. Therefore negative signals also work. Like with inserters, the signals from red and green are added first.
Due to the inherently laggy nature of circuits, I would recommend keeping the number of connected belts low, use this for junctions, not to turn your entire main bus around.