The installation of rear fog lamps is regulated by European standards. According to them, you can only install one counter to the rear. The power of this headlamp shall exceed the power of the position lamps. The fog lamp shall be on the left side of the vehicles that are used in the right-hand drive countries. Therefore, the position intended for the fog lamp on the right side is intended for cars sold in countries with left-hand traffic.
The logic of this standard is that in the case of rain or fog, the two burning rear fog-headlights of a car ahead can be easily confused with stop lamps.
