When may a strobe light be activated on a vehicle?

Activating a strobe light on a vehicle is essential for enhancing visibility and safety in specific situations. The correct answer pertains to when visibility is significantly reduced, which often occurs in conditions such as heavy fog, rain, or snow. Reducing visibility to 500 feet signals a serious decline in driving conditions, where the strobe light can help alert other drivers and increase the visibility of the vehicle. This is crucial in ensuring the safety of the vehicle and its passengers, particularly in scenarios where being seen can prevent accidents.

In contrast, the other options do not align with the standard usage guidelines for strobe lights. Parking on the side of the road, for example, typically does not necessitate the use of a strobe light unless there's a specific hazard or a legal requirement in that area. Traveling under 25 mph generally does not impact visibility enough to warrant a strobe light, and limiting the use of strobe lights to daylight hours ignores the fact that their primary function is to aid visibility in low light conditions, which can occur at any time of day.