During daylight hours, a vehicle with a load extending beyond the rear by __________ feet must display a red flag.

A vehicle that has a load extending beyond the rear by four feet must display a red flag during daylight hours to ensure visibility and safety. This requirement is crucial for alerting other drivers to the presence of an extended load, thereby reducing the risk of accidents. A red flag serves as a clear signal that the vehicle may be wider or longer than usual, giving other road users sufficient time to react appropriately.

In contrast, a distance of two, three, or five feet does not align with the established regulations, which specifically state that four feet is the threshold. Using a flag in these defined circumstances helps ensure that safety protocols are followed and enhances awareness on the road, leading to safer travel for all vehicle operators.