These days many intersections with traffic signals (at least in Vancouver, where I live) are not on a cycle where they constantly run for a certain amount of time in each direction. Instead, these signals are controlled by wires under the street. Often these signals involve a special left-turn advance signal for cars.
You can see these wires, which are usually in a circle, as you approach many intersections. When your car is over this circle, because of some mysterious magnetic properties or whatever, the light will change if it is currently red in your direction.
Now, in many places, there is only one circle at the intersection, because it isn't deemed necessary to change the lights so you get an advanced left-turn. The people designing these intersections figure that you can just wait until the green light which you get turns to yellow. Or sometimes if there is only one circle, the advanced left-turn will ALWAYS come on.
BUT ... in many situations, where there would often be more than one car turning left at these intersections, there is a circle for the first car, and also a circle for the THIRD car (two cars do not deem enough attention; they can both wait until the light turns yellow).
Now, if someone is at the first circle and there is no one after them, and there is a third circle, and you stop over the third circle (assuming no one is behind you, in which case you should move forward and let THEM be over the third circle), then you will cause the advanced left-turn signal to be activated and you can get a priority left turn!
Isn't that GENIUS?!?