You are driving during the day and it starts to rain torrentially, severely reducing visibility, as shown in the image. Must you turn on the rear fog lights?

Why this is the correct answer

Yes, turning on the rear fog light is compulsory in this situation. Spanish traffic rules make a critical distinction between two levels of bad weather: 1. **Heavy rain** ("lluvia intensa"): You must use dipped headlights (and optionally front fog lights), but the rear fog light must NOT be switched on — it would dazzle drivers behind you and could result in a fine. 2. **Very heavy / torrential rain** ("lluvia muy intensa") that severely reduces visibility — as shown in the image: The rear fog light MUST be switched on. This also applies to thick fog, heavy snowfall, or dense clouds of dust or smoke. The word "very" ("muy") makes all the difference in the exam. If the question says just "heavy rain" without mentioning extreme visibility loss, the rear fog light is NOT compulsory. But when the rain is torrential and visibility is severely reduced (as pictured), it IS compulsory — so that drivers behind you can see your vehicle in time. Remember: always turn off the rear fog light as soon as conditions improve, because its intense red glow can dazzle and confuse following drivers.