Which violation involves not maintaining a safe distance from the vehicle in front?

Maintaining a safe distance from the vehicle in front is crucial for safe driving as it allows for adequate reaction time in the event of sudden stops or emergencies. The violation known as "following too closely" specifically addresses this issue. When a driver follows another vehicle too closely, they compromise their ability to react safely, potentially leading to rear-end collisions, which are among the most common types of accidents.

Traffic laws often specify the required following distance based on speed and road conditions, ensuring drivers have enough space to stop safely if the vehicle ahead slows down or stops unexpectedly. By recognizing and adhering to this rule, drivers contribute to safer road conditions for themselves and others.

The other options focus on different driving behaviors, such as lane changes, turns, and U-turns, which do not directly pertain to the act of maintaining distance from the vehicle ahead. Thus, "following too closely" is the correct choice pertaining specifically to safe following distance.