When must a driver use a turn indicator?

Answer: C — To pass another vehicle or change lanes

Using a turn indicator, commonly known as a turn signal, is essential for communicating your intentions to other road users. This improves safety by making it clear when a driver plans to change lanes or pass another vehicle. Proper use of turn indicators helps to avoid misunderstandings and potential accidents, as other drivers can anticipate your actions. In the context of passing or changing lanes, signaling is not just a courtesy; it's a rule that reinforces the principle of safe driving. By indicating your intention to pass another vehicle or change lanes, you provide critical information that can prevent collisions and enhance overall road safety. While there are rules for using turn indicators in other scenarios such as exiting a highway or backing up, the practice of signaling during lane changes and passing is particularly emphasized due to the dynamic nature of traffic in those situations. This becomes even more significant in environments where quick decisions and movements are common.