Why can oncoming vehicles go straight when the left turn light is green?

[GenesisAnn]

Oncoming vehicles can go straight when the left turn light is green because at intersections with only red, yellow, and green lights, vehicles can proceed in three directions when the green light is on. When going straight while both left turn and straight lights are green: This will be penalized as driving not in the specified direction, resulting in a fine and 2 demerit points. The rules for combined left turn and straight lanes depend on the direction of travel. If you need to turn left, check if the left turn signal is green; if you want to go straight, check if the straight light is green. When going straight while the straight light is green and the left turn light is red: This is usually treated as running a red light, resulting in a fine and 6 demerit points. If a left-turning vehicle causes an accident when there are no traffic signals, signs, or police officers, and it proceeds ahead of straight-going vehicles at the intersection, the left-turning vehicle will bear full responsibility.