What action is considered a violation for not properly backing up?

Unsafe backing on a highway is a violation due to the inherent risks associated with maneuvering in such environments. Highways are designed for higher speeds, and improper backing can lead to serious accidents. When backing up on a highway, drivers must ensure they are aware of their surroundings, including oncoming traffic and road conditions. Given that drivers have less time to react at higher speeds, any unsafe maneuver can endanger not only the driver but also other motorists. This type of action poses significant safety concerns, as it disrupts the flow of traffic and increases the likelihood of collisions.

The other options involve different types of infractions that do not specifically pertain to the act of backing up or the dangers associated with it in a highway context. Making a U-turn on a curve can be dangerous, but it does not relate to backing. Following too closely, while important for maintaining safe following distances, does not involve the act of backing. Failing to signal is a violation related to communication with other drivers but does not pertain to the specific action of backing up. Therefore, the focus on the unique dangers of improper backing on a highway makes it the clear violation in this scenario.