Many drivers switch on their hazard lights when traffic suddenly slows or stops, warning vehicles behind them of a possible collision. But Spain’s General Traffic Regulations specify a different way to signal a substantial reduction in speed, including when it is caused by traffic conditions.
Article 109 says drivers should, whenever possible, give repeated brake-light signals or move an arm quickly up and down. The rule does not prescribe hazard lights for this situation. It also recognises that the signals may not always be practical: drivers may need to keep both hands on the wheel, and flashing the brake lights can require releasing and pressing the pedal again.
The article says drivers are not prohibited from using hazard lights to warn of a sudden queue, and they are not fined for failing to use the specified signals when doing so is not possible. The source notes that many newer cars activate hazard lights automatically during hard, sudden braking.
The regulations do require hazard lights in a separate circumstance. Under Article 49, drivers must use them while moving if their vehicle cannot reach the road’s minimum required speed and there is a risk of being hit from behind.
Sources: Motorpasión.